Question

question 19 (1 point)
for the given triangle, cos a is equal to which expression?
20 cm
a
15 cm
a) $\frac{4}{3}$
b) $\frac{3}{5}$
c) $\frac{4}{5}$
d) $\frac{3}{4}$

Explanation:

<Step1: Find the hypotenuse using Pythagoras' theorem>

$$\begin{align*} \text{Hypotenuse}^2&=15^2 + 20^2\\ &=225+400\\ &=625\\ \text{Hypotenuse}&=\sqrt{625}=25 \end{align*}$$

<Step2: Use the cosine formula>

$$ \cos A=\frac{\text{Adjacent side}}{\text{Hypotenuse}}=\frac{15}{25}=\frac{3}{5} $$

Answer:

B. $\frac{3}{5}$