Evaluate -cos(-pi)

$- \cos (- π)$

Step 1

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 2

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

$- (- 1 \cdot 1)$

Step 3

Multiply $- (- 1 \cdot 1)$ .

Multiply $- 1$ by $1$ .

$- - 1$

Multiply $- 1$ by $- 1$ .

$1$

Evaluate -cos(-pi)

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