Q. 12 - Precalculus Enhanced with Graphing Utilities

Question

In problems 11-26, use the fact that the trigonometric function are periodic to find the exact value of each expression. Do not use a calculator.

$\cos \left(420°\right)$

Step-by-Step Solution

Answer

The exact value is $\frac{1}{2}$.

Step 1. Given information.

We have:

$\cos 420°$

Step 2. Find the exact value of trigonometric function.

The function is $\cos 420°$.

Formula used:

$\cos \left(\theta +2\pi \right)=\cos \theta$

Here, $\theta =60°$

$$\begin{gathered} \cos \left(60°+360°\right)=\cos 60° \\ =\frac{1}{2} \end{gathered}$$