Precalculus Examples

$\cos (x)$ , $x = 7 π$

Step 1

Replace the variable $x$ with $7 π$ in the expression.

$\cos (7 π)$

Step 2

Subtract full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$\cos (π)$

Step 3

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.

$- \cos (0)$

Step 4

The exact value of $\cos (0)$ is $1$ .

$- 1 \cdot 1$

Step 5

Multiply $- 1$ by $1$ .

$- 1$

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