Precalculus : Solve a Right Triangle

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #11 : Solve A Right Triangle

Find the area of the given isosceles triangle:

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Possible Answers:

\displaystyle 24.5\; cm^{2}

\displaystyle 67.32 \; cm^{2}

\displaystyle 49 \; cm^{2}

\displaystyle 35.7 \; cm^{2}

\displaystyle 17.85\; cm^{2}

Correct answer:

\displaystyle 17.85\; cm^{2}

Explanation:

The first step is to divide this isosceles triangle into 2 right triangles, making it easier to solve:

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The equation for area is \displaystyle A=\frac{1}{2}base\cdot height

We already know the base, so we need to solve for height to get the area. 

\displaystyle tan20^{\circ}=\frac{height}{7\; cm}

\displaystyle 0.364=\frac{height}{7\; cm}

\displaystyle height=2.55\; cm

Then we plug in all values for the equation:

\displaystyle Area=\frac{1}{2}\cdot14\; cm\cdot2.55\; cm=17.85\; cm^{2}

Example Question #12 : Solve A Right Triangle

Find the area of the given isosceles triangle:

Varsity log graph

Possible Answers:

\displaystyle 6.25 \: cm^{2}

\displaystyle 3.11 \: cm^{2}

\displaystyle 25.55\: cm^{2}

\displaystyle 3.34 \: cm^{2}

\displaystyle 6.71 \: cm^{2}

Correct answer:

\displaystyle 6.25 \: cm^{2}

Explanation:

The first step toward finding the area is to divide this isosceles triangle into two right triangles:

Varsity log graph

Trigonometric ratios can be used to find both the height and the base, which are needed to calculate area:

\displaystyle sin(75^{\circ})=\frac{height}{5\: cm}

\displaystyle 0.9659=\frac{height}{5\: cm}

\displaystyle height=4.83\: cm

\displaystyle sin(15^{\circ})=\frac{1/2base}{5\: cm}

\displaystyle 0.2588=\frac{1/2base}{5\: cm}

\displaystyle Base=2.59\: cm

With both of those values calculated, we can now calculate the area of the triangle:

\displaystyle Area=\frac{1}{2}\cdot2.59\: cm\cdot4.83\: cm=6.25\: cm^2

Example Question #13 : Solve A Right Triangle

Pcq1

Solve the right triangle given that a=5, b=12, and A=22.620°

Possible Answers:

B=67.380°

C=90°

c=13

B=67.380°

C=90°

c=17

B=90°

C=67.380°

c=13

B=90°

C=67.380°

c=169

None of these answers are correct.

Correct answer:

B=67.380°

C=90°

c=13

Explanation:

Pcq1

C is given as 90°.

A is given as 22.620°

a is given as 5

b is given as 12

 

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

Therefore...

\displaystyle 5^{2}+12^{2}=c^{2}

\displaystyle 169=c^{2}

\displaystyle \sqrt{169}=\sqrt{c^{2}}

\displaystyle 13=c

 

All angles of a triangle add up to equal 180°.

\displaystyle 90^{\circ}+22.620^{\circ}+B=180^{\circ}

\displaystyle 112.620^{\circ}+B=180^{\circ}

\displaystyle B=180^{\circ}-112.620^{\circ}

\displaystyle B=67.380^{\circ}

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