Trigonometry Examples

$\sin (\frac{3 π}{2} + θ)$

Step 1

Use the sum formula for sine to simplify the expression. The formula states that $\sin (A + B) = \sin (A) \cos (B) + \cos (A) \sin (B)$ .

$\sin (\frac{3 π}{2}) \cos (θ) + \cos (\frac{3 π}{2}) \sin (θ)$

Step 2

Remove parentheses.

$\sin (\frac{3 π}{2}) \cos (θ) + \cos (\frac{3 π}{2}) \sin (θ)$

Step 3

Simplify each term.

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Step 3.1

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 fourth quadrant.

$- \sin (\frac{π}{2}) \cos (θ) + \cos (\frac{3 π}{2}) \sin (θ)$

Step 3.2

The exact value of $\sin (\frac{π}{2})$ is $1$ .

$- 1 \cdot 1 \cos (θ) + \cos (\frac{3 π}{2}) \sin (θ)$

Step 3.3

Multiply $- 1$ by $1$ .

$- 1 \cos (θ) + \cos (\frac{3 π}{2}) \sin (θ)$

Step 3.4

Rewrite $- 1 \cos (θ)$ as $- \cos (θ)$ .

$- \cos (θ) + \cos (\frac{3 π}{2}) \sin (θ)$

Step 3.5

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.

$- \cos (θ) + \cos (\frac{π}{2}) \sin (θ)$

Step 3.6

The exact value of $\cos (\frac{π}{2})$ is $0$ .

$- \cos (θ) + 0 \sin (θ)$

Step 3.7

Multiply $0$ by $\sin (θ)$ .

$- \cos (θ) + 0$

Step 4

Add $- \cos (θ)$ and $0$ .

$- \cos (θ)$