Trigonometry Examples

$(\sec (x) + \tan (x)) (\sec (x) - \tan (x)) = 1$

Step 1

Start on the left side.

$(\sec (x) + \tan (x)) (\sec (x) - \tan (x))$

Step 2

Simplify the expression.

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Step 2.1

Simplify each term.

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Step 2.1.1

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

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

Step 2.1.2

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

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

Step 2.2

Simplify each term.

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Step 2.2.1

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

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

Step 2.2.2

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

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

Step 2.3

Expand $(\frac{1}{\cos (x)} + \frac{\sin (x)}{\cos (x)}) (\frac{1}{\cos (x)} - \frac{\sin (x)}{\cos (x)})$ using the FOIL Method.

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Step 2.3.1

Apply the distributive property.

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

Step 2.3.2

Apply the distributive property.

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

Step 2.3.3

Apply the distributive property.

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

Step 2.4

Combine the opposite terms in $\frac{1}{\cos (x)} \cdot \frac{1}{\cos (x)} + \frac{1}{\cos (x)} (- \frac{\sin (x)}{\cos (x)}) + \frac{\sin (x)}{\cos (x)} \cdot \frac{1}{\cos (x)} + \frac{\sin (x)}{\cos (x)} (- \frac{\sin (x)}{\cos (x)})$ .

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Step 2.4.1

Reorder the factors in the terms $\frac{1}{\cos (x)} (- \frac{\sin (x)}{\cos (x)})$ and $\frac{\sin (x)}{\cos (x)} \cdot \frac{1}{\cos (x)}$ .

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

Step 2.4.2

Add $- \frac{1}{\cos (x)} \cdot \frac{\sin (x)}{\cos (x)}$ and $\frac{1}{\cos (x)} \cdot \frac{\sin (x)}{\cos (x)}$ .

$\frac{1}{\cos (x)} \cdot \frac{1}{\cos (x)} + 0 + \frac{\sin (x)}{\cos (x)} (- \frac{\sin (x)}{\cos (x)})$

Step 2.4.3

Add $\frac{1}{\cos (x)} \cdot \frac{1}{\cos (x)}$ and $0$ .

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

Step 2.5

Simplify each term.

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Step 2.5.1

Multiply $\frac{1}{\cos (x)} \cdot \frac{1}{\cos (x)}$ .

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Step 2.5.1.1

Multiply $\frac{1}{\cos (x)}$ by $\frac{1}{\cos (x)}$ .

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

Step 2.5.1.2

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

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

Step 2.5.1.3

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

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

Step 2.5.1.4

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

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

Step 2.5.1.5

Add $1$ and $1$ .

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

Step 2.5.2

Rewrite using the commutative property of multiplication.

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

Step 2.5.3

Multiply $- \frac{\sin (x)}{\cos (x)} \cdot \frac{\sin (x)}{\cos (x)}$ .

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Step 2.5.3.1

Multiply $\frac{\sin (x)}{\cos (x)}$ by $\frac{\sin (x)}{\cos (x)}$ .

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

Step 2.5.3.2

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

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

Step 2.5.3.3

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

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

Step 2.5.3.4

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

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

Step 2.5.3.5

Add $1$ and $1$ .

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

Step 2.5.3.6

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

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

Step 2.5.3.7

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

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

Step 2.5.3.8

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

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

Step 2.5.3.9

Add $1$ and $1$ .

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

Step 2.6

Combine the numerators over the common denominator.

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

Step 2.7

Apply pythagorean identity.

$\frac{\cos^{2} (x)}{\cos^{2} (x)}$

Step 2.8

Cancel the common factor of $\cos^{2} (x)$ .

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Step 2.8.1

Cancel the common factor.

$\frac{\cos^{2} (x)}{\cos^{2} (x)}$

Step 2.8.2

Rewrite the expression.

$1$

Step 3

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

$(\sec (x) + \tan (x)) (\sec (x) - \tan (x)) = 1$ is an identity