Trigonometry Examples

$\cos (x) (\sec (x) - \cos (x)) = \sin^{2} (x)$

Step 1

Start on the left side.

$\cos (x) (\sec (x) - \cos (x))$

Step 2

Simplify the expression.

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Step 2.1

Rewrite $\sec (x)$ in terms of sines and cosines.

$\cos (x) (\frac{1}{\cos (x)} - \cos (x))$

Step 2.2

Apply the distributive property.

$\cos (x) \frac{1}{\cos (x)} + \cos (x) (- \cos (x))$

Step 2.3

Cancel the common factor of $\cos (x)$ .

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Step 2.3.1

Cancel the common factor.

$\cos (x) \frac{1}{\cos (x)} + \cos (x) (- \cos (x))$

Step 2.3.2

Rewrite the expression.

$1 + \cos (x) (- \cos (x))$

Step 2.4

Rewrite using the commutative property of multiplication.

$1 - \cos (x) \cos (x)$

Step 2.5

Multiply $- \cos (x) \cos (x)$ .

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Step 2.5.1

Raise $\cos (x)$ to the power of $1$ .

$1 - (\cos^{1} (x) \cos (x))$

Step 2.5.2

Raise $\cos (x)$ to the power of $1$ .

$1 - (\cos^{1} (x) \cos^{1} (x))$

Step 2.5.3

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$1 - {\cos (x)}^{1 + 1}$

Step 2.5.4

Add $1$ and $1$ .

$1 - \cos^{2} (x)$

Step 2.6

Apply pythagorean identity.

$\sin^{2} (x)$

Step 3

Because the two sides have been shown to be equivalent, the equation is an identity.

$\cos (x) (\sec (x) - \cos (x)) = \sin^{2} (x)$ is an identity