Trigonometry Examples

$\cos (π - x)$

Step 1

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

$\cos (π) \cdot \cos (x) + \sin (π) \cdot \sin (x)$

Step 2

Remove parentheses.

$\cos (π) \cdot \cos (x) + \sin (π) \cdot \sin (x)$

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 cosine is negative in the second quadrant.

$- \cos (0) \cdot \cos (x) + \sin (π) \cdot \sin (x)$

Step 3.2

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

$- 1 \cdot 1 \cdot \cos (x) + \sin (π) \cdot \sin (x)$

Step 3.3

Multiply $- 1$ by $1$ .

$- 1 \cdot \cos (x) + \sin (π) \cdot \sin (x)$

Step 3.4

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

$- \cos (x) + \sin (π) \cdot \sin (x)$

Step 3.5

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

$- \cos (x) + \sin (0) \cdot \sin (x)$

Step 3.6

The exact value of $\sin (0)$ is $0$ .

$- \cos (x) + 0 \cdot \sin (x)$

Step 3.7

Multiply $0$ by $\sin (x)$ .

$- \cos (x) + 0$

Step 4

Add $- \cos (x)$ and $0$ .

$- \cos (x)$