Basic Geometry : How to find the area of a right triangle

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

Example Question #1 : How To Find The Area Of A Right Triangle

Righttriangle

Given:

A = 3 cm

B = 4 cm

What is the area of the right triangle ABC? 

Possible Answers:

7 square centimeters

13 square centimeters

6 square centimeters

12 square centimeters

5 square centimeters

Correct answer:

6 square centimeters

Explanation:

The area of a triangle is given by the equation:

\displaystyle A_{\Delta } = (1/2)*(base)*(height)

Since the base leg of the given triangle is 4 cm, while the height is 3 cm, this gives:

\displaystyle A_{\Delta }=(1/2)*3*4 = 6 cm^{2}

Example Question #1 : How To Find The Area Of A Right Triangle

Righttriangle

Given:

A = 4 cm

B = 6 cm

What is the area of the right triangle ABC? 

Possible Answers:

11 square centimeters

8 square centimeters

12 square centimeters

10 square centimeters

24 square centimeters

Correct answer:

12 square centimeters

Explanation:

The area of a triangle is given by the equation:

\displaystyle A_{\Delta } = (1/2)*(base)*(height)

Since the base leg of the given triangle is 4 cm, while the height is 3 cm, this gives:

\displaystyle A_{\Delta }=(1/2)*4*6 = 12 cm^{2}

Example Question #2 : How To Find The Area Of A Right Triangle

Righttriangle

Given:

A = 3 cm

B = 7 cm

What is the area of the triangle? 

Possible Answers:

10 square centimeters

8.3 square centimeters

10.5 square centimeters

7 square centimeters

7.6 square centimeters

Correct answer:

10.5 square centimeters

Explanation:

The area of a triangle is given by the equation:

\displaystyle A_{\Delta } = (1/2)*(base)*(height)

Since the base leg of the given triangle is 4 cm, while the height is 3 cm, this gives:

\displaystyle A_{\Delta }=(1/2)*3*7 = 10.5 cm^{2}

Example Question #3 : How To Find The Area Of A Right Triangle

Righttriangle

Given that:

A = 6 cm

B = 10 cm

What is the area of the right trianlge ABC?

Possible Answers:

35 square centimeters

90 square centimeters

60 square centimeters

30 square centimeters

16 square centimeters

Correct answer:

30 square centimeters

Explanation:

The area of a triangle is given by the equation:

\displaystyle A_{\Delta } = (1/2)*(base)*(height)

Since the base leg of the given triangle is 4 cm, while the height is 3 cm, this gives:

\displaystyle A_{\Delta }=(1/2)*10*6 = 12 cm^{2}

Example Question #4 : How To Find The Area Of A Right Triangle

Righttriangle

Given that:

A = 3 cm

B = 4 cm

C = 5 cm

What is the area of the right triangle ABC? 

Possible Answers:

10 square centimeters

7 square centimeters

6.5 square centimeters

12 square centimeters

6 square centimeters

Correct answer:

6 square centimeters

Explanation:

The area of a triangle is given by the equation:

\displaystyle A_{\Delta } = (1/2)*(base)*(height)

Since the base leg of the given triangle is 4 cm, while the height is 3 cm, this gives:

\displaystyle A_{\Delta }=(1/2)*4*3 = 6 cm^{2}

Example Question #5 : How To Find The Area Of A Right Triangle

Righttriangle

Given that:

A = 10 cm 

B = 20 cm

What is the area of the right triangle ABC?

Possible Answers:

70 square centimeters

50 square centimeters

30 square centimeters

120 square centimeters

100 square centimeters

Correct answer:

100 square centimeters

Explanation:

The area of a triangle is given by the equation:

\displaystyle A_{\Delta } = (1/2)*(base)*(height)

Since the base leg of the given triangle is 4 cm, while the height is 3 cm, this gives:

\displaystyle A_{\Delta }=(1/2)*20*10 = 100 cm^{2}

Example Question #6 : How To Find The Area Of A Right Triangle

The length of the legs of the triangle below (not to scale) are as follows:

\displaystyle a=7 cm

\displaystyle b=12 cm

Right_triangle_with_labeled_sides 

What is the area of the triangle?

Possible Answers:

\displaystyle 84 square centimeters

\displaystyle 28 square centimeters

\displaystyle 42 square centimeters

\displaystyle \sqrt{193} square centimeters

\displaystyle 42 linear centimeters

Correct answer:

\displaystyle 42 square centimeters

Explanation:

The formula for the area of a triangle is

 \displaystyle \frac{1}{2}bh

where \displaystyle b is the base of the triangle and \displaystyle h is the height.

For the triangle shown, side \displaystyle a is the base and side \displaystyle b is the height.

Therefore, the area is equal to

 \displaystyle \frac{1}{2}(7)(12)=42

or, based on the units given, 42 square centimeters

Example Question #1 : How To Find The Area Of A Right Triangle

An equilateral triangle has a side of \displaystyle 4\; in

What is the area of the triangle?

Possible Answers:

\displaystyle 6\; in^{2}

\displaystyle 4\sqrt{3}\; in^{2}

\displaystyle 2\sqrt{3}\; in^{2}

\displaystyle 8\; in^{2}

\displaystyle 2\sqrt{2}\; in^{2}

Correct answer:

\displaystyle 4\sqrt{3}\; in^{2}

Explanation:

An equilateral triangle has three congruent sides. The area of a triangle is given by \displaystyle A = \frac{1}{2}bh where \displaystyle b is the base and \displaystyle h is the height.

The equilateral triangle can be broken into two \displaystyle 30-60-90 right triangles, where the legs are \displaystyle 2 and \displaystyle x and the hypotenuses is \displaystyle 4.

Using the Pythagorean Theorem we get \displaystyle 4^{2}=2^{2} + x^{2} or \displaystyle x=2\sqrt{3} and the area is \displaystyle A = \frac{1}{2}bh= \frac{1}{2}(4)(2\sqrt{3}) = 4\sqrt{3}

Example Question #8 : How To Find The Area Of A Right Triangle

The hypotenuse of a \displaystyle 30^{\circ }-60^{\circ }-90^{\circ } triangle measures eight inches. What is the area of this triangle (radical form, if applicable)?

Possible Answers:

It is impossible to tell from the information given.

\displaystyle 16 \; \textrm{in}^{2}

\displaystyle 8\; \textrm{{in}}^{2}

\displaystyle 8\sqrt{3} \; \textrm{in}^{2}

\displaystyle 8\sqrt{2} \; \textrm{in}^{2}

Correct answer:

\displaystyle 8\sqrt{3} \; \textrm{in}^{2}

Explanation:

In a \displaystyle 30^{\circ }-60^{\circ }-90^{\circ }, the shorter leg is half as long as the hypotenuse, and the longer leg is \displaystyle \sqrt{3} times the length of the shorter. Since the hypotenuse is 8, the shorter leg is 4, and the longer leg is \displaystyle 4\sqrt{3}, making the area:

\displaystyle A = \frac{1}{2} bh = \frac{1}{2} \cdot 4 \cdot 4\sqrt{3} = 8\sqrt{3}

Example Question #1391 : Basic Geometry

Img052

\displaystyle What\;is\;the\;area\;of\;\Delta GHJ?

Possible Answers:

\displaystyle 30

\displaystyle 20

\displaystyle 60

\displaystyle 45

Correct answer:

\displaystyle 30

Explanation:

\displaystyle Area \;\Delta= \frac{1}{2}(base)(height)

\displaystyle \Delta GHF=\frac{1}{2}(5)(12)=\frac{1}{2}(60)=30

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