Basic Geometry : 45/45/90 Right Isosceles Triangles

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

Example Question #11 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 8?

Possible Answers:

\displaystyle 26.46

\displaystyle 28.19

\displaystyle 27.31

\displaystyle 29.02

Correct answer:

\displaystyle 27.31

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=8\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=8+8+8\sqrt2=27.31

Example Question #12 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 9?

Possible Answers:

\displaystyle 29.05

\displaystyle 40.99

\displaystyle 30.73

\displaystyle 18.15

Correct answer:

\displaystyle 30.73

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=9\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=9+9+9\sqrt2=30.73

Example Question #13 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 11?

Possible Answers:

\displaystyle 37.56

\displaystyle 39.71

\displaystyle 35.45

\displaystyle 38.87

Correct answer:

\displaystyle 37.56

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=11\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=11+11+11\sqrt2=37.56

Example Question #1114 : Basic Geometry

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 14?

Possible Answers:

\displaystyle 51.92

\displaystyle 47.71

\displaystyle 49.02

\displaystyle 47.80

Correct answer:

\displaystyle 47.80

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=14\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=14+14+14\sqrt2=47.80

Example Question #14 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 20?

Possible Answers:

\displaystyle 60.91

\displaystyle 99.28

\displaystyle 65.01

\displaystyle 68.28

Correct answer:

\displaystyle 68.28

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=20\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=20+20+20\sqrt2=68.28

Example Question #15 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 19?

Possible Answers:

\displaystyle 65.50

\displaystyle 68.12

\displaystyle 66.71

\displaystyle 64.87

Correct answer:

\displaystyle 64.87

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=19\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=19+19+19\sqrt2=64.87

Example Question #16 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 16?

Possible Answers:

\displaystyle 54.63

\displaystyle 59.42

\displaystyle 56.91

\displaystyle 55.87

Correct answer:

\displaystyle 54.63

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=16\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=16+16+16\sqrt2=54.63

Example Question #17 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 22?

Possible Answers:

\displaystyle 75.11

\displaystyle 72.01

\displaystyle 74.01

\displaystyle 78.91

Correct answer:

\displaystyle 75.11

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=4\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=22+22+22\sqrt2=75.11

Example Question #18 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

What is the perimeter of a right isosceles triangle with leg lengths of \displaystyle 13?

Possible Answers:

\displaystyle 48.21

\displaystyle 41.09

\displaystyle 42.42

\displaystyle 44.38

Correct answer:

\displaystyle 44.38

Explanation:

13

Recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+b+c

Now, because this is a right isosceles triangle, we know the following:

\displaystyle a=b

From the information given in the question, we already have two of the sides needed. Now, recall the Pythagorean Theorem to find the third side of the triangle, the hypotenuse.

\displaystyle a^2+b^2=c^2

The Pythagorean Theorem can then be simplifed to the following equation:

\displaystyle a^2+a^2=2a^2=c^2

Now, solve for \displaystyle c since the question asks for the length of the hypotenuse.

\displaystyle c=\sqrt{2a^2}

\displaystyle c=a\sqrt2

Now, plug in the given value for \displaystyle a to find the length of the hypotenuse.

\displaystyle c=13\sqrt2

Now that we have all three sides of the triangle, we can find the perimeter. Use a calculator and round to \displaystyle 2 decimal places.

\displaystyle \text{Perimeter}=13+13+13\sqrt2=44.38

Example Question #19 : How To Find The Perimeter Of A 45/45/90 Right Isosceles Triangle

Find the perimeter.

1

Possible Answers:

\displaystyle 35.99

\displaystyle 29.12

\displaystyle 45.06

\displaystyle 40.97

Correct answer:

\displaystyle 40.97

Explanation:

13

Notice that the given triangle is a right isosceles triangle. The two legs with the tick marks are the same length.

The lengths of the legs in the given triangle are then \displaystyle 12.

Next, find the length of the hypotenuse by using the Pythagorean Theorem.

\displaystyle a^2+a^2=b^2

\displaystyle b^2=2a^2

\displaystyle b=a\sqrt2

Plug in the value of the length of a leg to find the length of the hypotenuse.

\displaystyle b=12\sqrt2

Finally, recall how to find the perimeter of a triangle:

\displaystyle \text{Perimeter}=a+a+b

Plug in the values for this triangle to find its perimeter.

\displaystyle \text{Perimeter}=12+12+12\sqrt2=40.97

Make sure to round to two places after the decimal.

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