Apply Pythagorean Theorem to Problems
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8th Grade Math › Apply Pythagorean Theorem to Problems
A right triangle has a hypotenuse of 10 units and one leg of 6 units. What is the length of the other leg?
4 units
64 units
8 units
16 units
Explanation
This question tests applying the Pythagorean theorem a² + b² = c² to find an unknown leg with given hypotenuse and one leg. For a right triangle with hypotenuse c=10 units and leg a=6 units, the other leg b is b² = c² - a² = 100 - 36 = 64, so b = √64 = 8 units. In this specific problem, with hypotenuse 10 units and one leg 6 units, the other leg is √(10² - 6²) = √(100 - 36) = √64 = 8 units. The correct setup identifies the hypotenuse, subtracts the squared leg, and takes the square root, matching choice B. A common error is adding instead of subtracting, like 100 + 36 = 136, or not taking square root to choose 64. To solve: (1) identify the right triangle, (2) label hypotenuse 10 units, one leg 6 units, other b, (3) note hypotenuse and one leg known, (4) set up b² = 10² - 6², (5) calculate 100 - 36 = 64, b = √64 = 8 units, (6) verify it's reasonable as 8 is between 6 and 10. Common mistakes include mislabeling hypotenuse or errors in squaring like 6²=36 but 10²=100 correct.
In a right triangle, the hypotenuse is 13 m and one leg is 5 m. What is the length of the other leg?
144 m
18 m
8 m
12 m
Explanation
This question tests applying the Pythagorean theorem a² + b² = c² to find an unknown side in right triangles, such as 2D problems like ladders or diagonals, or 3D problems like space diagonals. For a right triangle with legs a and b, and hypotenuse c (the longest side opposite the 90° angle), if two sides are known, the third can be found using a² + b² = c²; for example, finding the hypotenuse by plugging in the legs like 6² + 8² = 36 + 64 = 100 = c², so c = √100 = 10, or finding a leg by rearranging to a² = c² - b², such as if c = 13 and b = 5, then a² = 169 - 25 = 144, so a = 12; in real-world scenarios, identify the right triangle, like a ladder against a wall forming a right angle, assign values such as base = 9 ft and ladder = 15 ft, and solve 9² + h² = 15² to get h = 12 ft. In this specific problem, the right triangle has a hypotenuse of 13 m and one leg of 5 m, so we find the other leg using a² = 13² - 5², giving 169 - 25 = 144, so a = √144 = 12 m. The correct setup involves identifying c = 13 m as the hypotenuse and b = 5 m as one leg, then rearranging to a² = c² - b², calculating the squares, subtracting, and taking the square root to get 12 m, which matches choice B. A common error might be subtracting incorrectly, like 13 - 5 = 8, or forgetting to take the square root and choosing 144 m, or confusing which side is the hypotenuse and using the formula wrong. To solve these problems, follow these steps: (1) identify the right triangle with a 90° angle, (2) label the sides with legs a and b forming the right angle and hypotenuse c opposite it as the longest side, (3) identify the knowns (hypotenuse and one leg) and unknown (other leg), (4) set up a² = c² - b², (5) calculate by squaring the knowns, subtracting, and taking the square root, (6) verify it makes sense, like 12 m being between 5 m and 13 m. Common mistakes include using a + b = c without squaring, misidentifying the hypotenuse, arithmetic errors in squaring or subtracting, or taking a negative square root.
A rectangular poster is 6 inches wide and 8 inches tall. What is the length of the diagonal across the poster?
14 in
10 in
100 in
7 in
Explanation
This question tests applying the Pythagorean theorem a² + b² = c² to find the diagonal of a rectangle, which forms a right triangle. For a rectangle 6 inches wide (a=6 in) and 8 inches tall (b=8 in), the diagonal d is the hypotenuse: d² = 6² + 8² = 36 + 64 = 100, so d = √100 = 10 in. In this specific poster problem, the diagonal across 6 in by 8 in is found using d = √(6² + 8²) = √(36 + 64) = √100 = 10 in. The correct setup treats the width and height as legs of a right triangle, adds their squares for d², and takes the square root, matching choice B. A common error is multiplying like 6 × 8 = 48, or adding without squaring to get 14, or choosing 100 without square root. To solve: (1) identify the right triangle formed by the diagonal, (2) label legs as 6 in and 8 in, diagonal as d (hypotenuse), (3) note both legs known, hypotenuse unknown, (4) set up 6² + 8² = d², (5) calculate 36 + 64 = 100, d = √100 = 10 in, (6) verify it's reasonable as 10 in is longer than both sides. Common mistakes include confusing diagonal with perimeter or arithmetic errors like 8² = 64 but adding to 100 incorrectly.
A rectangular classroom rug is 6 feet wide and 8 feet long. What is the length of the rug’s diagonal (corner to corner)?
100 ft
14 ft
10 ft
7 ft
Explanation
This problem tests applying the Pythagorean theorem a² + b² = c² to find an unknown side in right triangles, such as 2D problems like ladders or diagonals, or even 3D space diagonals. For a right triangle with legs a and b, and hypotenuse c (the longest side opposite the 90° angle), if two sides are known, the third can be found using a² + b² = c²; for example, to find the hypotenuse, plug in the legs like 6² + 8² = 36 + 64 = 100 = c², so c = √100 = 10, or to find a leg, rearrange to a² = c² - b², such as if c=13 and b=5, then a² = 169 - 25 = 144, so a=12. In real-world scenarios, identify the right triangle, like a ladder against a wall forming a right angle, assign values such as base=9 ft and ladder=15 ft, and solve with 9² + h² = 15² to get h=12 ft. In this specific rectangle problem, the rug is 6 ft wide and 8 ft long, so the diagonal is found using d² = 6² + 8² = 36 + 64 = 100, giving d = √100 = 10 ft. The correct setup involves recognizing the diagonal forms a right triangle with the sides 6 ft and 8 ft as legs, applying a² + b² = d², and calculating to get 10 ft. Common errors include multiplying like 6*8=48, mistaking 6² as 12, forgetting the square root and saying 100 ft, or treating it as a non-right triangle. To solve: (1) identify the right triangle formed by the diagonal, (2) label legs a=6 ft and b=8 ft, hypotenuse d unknown, (3) note two legs known, hypotenuse unknown, (4) set up a² + b² = d², (5) calculate 36 + 64 = 100, √100=10, (6) verify 10 ft is reasonable as it's longer than both sides. Common mistakes: a + b = d like 6+8=14, wrong hypotenuse, arithmetic errors in addition or squaring, or negative length.
A rectangular prism (box) has dimensions 3 cm by 4 cm by 12 cm. What is the length of the space diagonal from one corner of the box to the opposite corner?
13 cm
17 cm
15 cm
12 cm
Explanation
This question tests applying the Pythagorean theorem in 3D to find the space diagonal of a rectangular prism. For a box with dimensions 3 cm, 4 cm, 12 cm, the space diagonal d uses d² = 3² + 4² + 12² = 9 + 16 + 144 = 169, so d = √169 = 13 cm, extending the theorem to three dimensions. In this specific prism problem, the space diagonal from one corner to the opposite is √(3² + 4² + 12²) = √(9 + 16 + 144) = √169 = 13 cm. The correct setup squares all three dimensions, adds them, and takes the square root, matching choice A. A common error is using only two dimensions, like √(3² + 4²)=5, or confusing with surface diagonal to get 12.65 or similar. To solve: (1) identify the 3D right triangle path, (2) label dimensions as three perpendicular legs, (3) note all known, diagonal unknown, (4) set up d² = 3² + 4² + 12², (5) calculate 9 + 16 + 144 = 169, d = √169 = 13 cm, (6) verify it's reasonable as 13 cm is longer than the longest side 12 cm. Common mistakes include omitting one dimension or arithmetic like 12²=124.
A right triangle has legs of length 6 cm and 8 cm. What is the length of the hypotenuse?
100 cm
12 cm
10 cm
14 cm
Explanation
This question tests applying the Pythagorean theorem $a^2 + b^2 = c^2$ to find the unknown hypotenuse in a right triangle with given legs. For a right triangle with legs a=6 cm and b=8 cm, and hypotenuse c (the longest side opposite the 90° angle), plug the legs into the formula: $6^2 + 8^2 = 36 + 64 = 100 = c^2$, so c = $\sqrt{100}$ = 10 cm. In this specific problem, the right triangle has legs of 6 cm and 8 cm, so the hypotenuse is found using c = $\sqrt{(6^2 + 8^2)} = \sqrt{(36 + 64)} = \sqrt{100}$ = 10 cm. The correct setup involves identifying the legs as a and b, squaring them, adding, and taking the square root for c, which matches choice A. A common error is adding without squaring, like 6 + 8 = 14, or forgetting the square root and choosing 100 cm. To solve: (1) identify the right triangle, (2) label legs as 6 cm and 8 cm, hypotenuse as c, (3) note both legs known, hypotenuse unknown, (4) set up $6^2 + 8^2 = c^2$, (5) calculate 36 + 64 = 100, c = $\sqrt{100}$ = 10 cm, (6) verify it's reasonable as 10 cm is longer than both legs. Common mistakes include confusing legs with hypotenuse or arithmetic errors like $6^2 = 36$ but $8^2 = 68$ incorrectly.
In a right triangle, the hypotenuse is 13 units and one leg is 5 units. What is the length of the other leg?
18 units
12 units
144 units
8 units
Explanation
This problem tests applying the Pythagorean theorem $a^2 + b^2 = c^2$ to find an unknown side in right triangles, such as 2D problems like ladders or diagonals, or even 3D space diagonals. For a right triangle with legs a and b, and hypotenuse c (the longest side opposite the 90° angle), if two sides are known, the third can be found using $a^2 + b^2 = c^2$; for example, to find the hypotenuse, plug in the legs like $6^2 + 8^2 = 36 + 64 = 100 = c^2$, so $c = \sqrt{100} = 10$, or to find a leg, rearrange to $a^2 = c^2 - b^2$, such as if c=13 and b=5, then $a^2 = 169 - 25 = 144$, so a=12. In real-world scenarios, identify the right triangle, like a ladder against a wall forming a right angle, assign values such as base=9 ft and ladder=15 ft, and solve with $9^2 + h^2 = 15^2$ to get h=12 ft. In this specific problem, the right triangle has hypotenuse 13 units and one leg 5 units, so the other leg is found using $a^2 = 13^2 - 5^2 = 169 - 25 = 144$, giving a = $\sqrt{144}$ = 12 units. The correct setup involves identifying the hypotenuse as c=13 and leg b=5, rearranging the formula to $a^2 = c^2 - b^2$, and calculating the square root to get 12 units. Common errors include subtracting without squaring like 13-5=8, mistaking 5² as 10, forgetting the square root and saying 144 units, or confusing the hypotenuse and using it as a leg. To solve: (1) identify the right triangle with the 90° angle implied, (2) label legs a (unknown) and b=5, hypotenuse c=13 as the longest, (3) note hypotenuse and one leg known, other leg unknown, (4) set up $a^2 = c^2 - b^2$, (5) calculate 169 - 25 = 144, $\sqrt{144}=12$, (6) verify $5^2 + 12^2 = 25 + 144 = 169 = 13^2$. Common mistakes: using a + b = c forgetting squares, wrong side as hypotenuse like treating 5 as c, arithmetic errors in subtraction or square root, or negative length.
A right triangle has legs 8 inches and 15 inches. What is the length of the hypotenuse?
7 in
120 in
23 in
17 in
Explanation
This problem tests applying the Pythagorean theorem $a^2 + b^2 = c^2$ to find an unknown side in right triangles, such as 2D problems like ladders or diagonals, or even 3D space diagonals. For a right triangle with legs a and b, and hypotenuse c (the longest side opposite the 90° angle), if two sides are known, the third can be found using $a^2 + b^2 = c^2$; for example, to find the hypotenuse, plug in the legs like $6^2 + 8^2 = 36 + 64 = 100 = c^2$, so $c = \sqrt{100} = 10$, or to find a leg, rearrange to $a^2 = c^2 - b^2$, such as if c=13 and b=5, then $a^2 = 169 - 25 = 144$, so a=12. In real-world scenarios, identify the right triangle, like a ladder against a wall forming a right angle, assign values such as base=9 ft and ladder=15 ft, and solve with $9^2 + h^2 = 15^2$ to get h=12 ft. In this specific problem, the right triangle has legs 8 in and 15 in, so the hypotenuse is found using $c^2 = 8^2 + 15^2 = 64 + 225 = 289$, giving $c = \sqrt{289} = 17$ in. The correct setup involves identifying legs a=8 and b=15, applying $a^2 + b^2 = c^2$, and calculating the square root to get 17 in. Common errors include adding without squaring like 8+15=23, mistaking 8² as 16, forgetting the square root and saying 289 in, or confusing hypotenuse with a leg. To solve: (1) identify the right triangle with 90° implied, (2) label legs a=8 in and b=15 in, hypotenuse c unknown, (3) note two legs known, hypotenuse unknown, (4) set up $a^2 + b^2 = c^2$, (5) calculate 64 + 225 = 289, $\sqrt{289}=17$, (6) verify 17 in is reasonable as longest side. Common mistakes: $a + b = c$ (23 in), wrong hypotenuse, arithmetic errors in addition or root, negative values.
In a right triangle, the hypotenuse is 13 m and one leg is 5 m. What is the length of the other leg?
12 m
18 m
144 m
8 m
Explanation
This question tests applying the Pythagorean theorem a² + b² = c² to find an unknown leg in a right triangle with given hypotenuse and one leg. For a right triangle with hypotenuse c=13 m and leg b=5 m, rearrange to a² = c² - b²: a² = 169 - 25 = 144, so a = √144 = 12 m. In this specific problem, with hypotenuse 13 m and one leg 5 m, the other leg is found using a = √(13² - 5²) = √(169 - 25) = √144 = 12 m. The correct setup involves identifying the hypotenuse as the longest side, subtracting the squared leg from the squared hypotenuse, and taking the square root, matching choice B. A common error is subtracting incorrectly or using addition like 13 + 5 = 18, or not taking the square root and choosing 144 m. To solve: (1) identify the right triangle, (2) label hypotenuse as 13 m, one leg as 5 m, other as a, (3) note hypotenuse and one leg known, other leg unknown, (4) set up a² = 13² - 5², (5) calculate 169 - 25 = 144, a = √144 = 12 m, (6) verify it's reasonable as 12 m is between 5 m and 13 m. Common mistakes include treating the given leg as hypotenuse or arithmetic errors like 13² = 179.
On a coordinate plane, point $A$ is at $(0,0)$ and point $B$ is at $(9,12)$. What is the distance from $A$ to $B$?
3
15
21
225
Explanation
This problem tests applying the Pythagorean theorem a² + b² = c² to find an unknown side in right triangles, such as 2D problems like ladders or diagonals, or even 3D space diagonals. For a right triangle with legs a and b, and hypotenuse c (the longest side opposite the 90° angle), if two sides are known, the third can be found using a² + b² = c²; for example, to find the hypotenuse, plug in the legs like 6² + 8² = 36 + 64 = 100 = c², so c = √100 = 10, or to find a leg, rearrange to a² = c² - b², such as if c=13 and b=5, then a² = 169 - 25 = 144, so a=12. In real-world scenarios, identify the right triangle, like a ladder against a wall forming a right angle, assign values such as base=9 ft and ladder=15 ft, and solve with 9² + h² = 15² to get h=12 ft. In this specific coordinate problem, points A(0,0) and B(9,12) form a right triangle with legs 9 and 12 (differences in x and y), so distance d = √(9² + 12²) = √(81 + 144) = √225 = 15. The correct setup involves recognizing the distance formula as Pythagorean theorem with Δx=9 and Δy=12 as legs, calculating to get 15. Common errors include adding coordinates like 0+9=9, mistaking differences, forgetting square root and saying 225, or not squaring. To solve: (1) identify right triangle from axes, (2) label legs Δx=9 and Δy=12, hypotenuse d, (3) note legs known, d unknown, (4) set up d² = Δx² + Δy², (5) calculate 81 + 144 = 225, √225=15, (6) verify 15 is reasonable. Common mistakes: a + b = d like 9+12=21, arithmetic errors, wrong differences, negative values.