Trigonometry Examples

$5 \cos (- 90)$

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 third quadrant.

$5 (- \cos (90))$

Step 2

The exact value of $\cos (90)$ is $0$ .

$5 (- 0)$

Step 3

Multiply $5 (- 0)$ .

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Step 3.1

Multiply $- 1$ by $0$ .

$5 \cdot 0$

Step 3.2

Multiply $5$ by $0$ .

$0$