Question

sine cosine tangent which trig function do you use?

Explanation:

Step1: Recall trig - function definitions

In a right - triangle, $\sin\theta=\frac{\text{opposite}}{\text{hypotenuse}}$, $\cos\theta=\frac{\text{adjacent}}{\text{hypotenuse}}$, $\tan\theta=\frac{\text{opposite}}{\text{adjacent}}$.

Step2: Identify sides in the triangle

Let the angle be $\theta = 65^{\circ}$, the side opposite to the $65^{\circ}$ angle is not given, the side adjacent to the $65^{\circ}$ angle is $x$, and the hypotenuse is $19$.

Step3: Determine the trig - function

We know the hypotenuse and the adjacent side to the given angle. The cosine function relates the adjacent side and the hypotenuse. So we use the cosine function, $\cos\theta=\frac{\text{adjacent}}{\text{hypotenuse}}$, i.e., $\cos65^{\circ}=\frac{x}{19}$.

Answer:

Cosine