Trigonometry Examples

$\sin (- 90 °)$

Step 1

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

$- \sin (90)$

Step 2

The exact value of $\sin (90)$ is $1$ .

$- 1 \cdot 1$

Step 3

Multiply $- 1$ by $1$ .

$- 1$