Precalculus Examples

${(4 \cos (x) - 7 \sin (x))}^{2} + {(7 \cos (x) + 4 \sin (x))}^{2} = 65$

Step 1

Square both sides of the equation.

${({(4 \cos (x) - 7 \sin (x))}^{2} + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2

Simplify ${({(4 \cos (x) - 7 \sin (x))}^{2} + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2}$ .

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Step 2.1

Simplify each term.

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Step 2.1.1

Rewrite ${(4 \cos (x) - 7 \sin (x))}^{2}$ as $(4 \cos (x) - 7 \sin (x)) (4 \cos (x) - 7 \sin (x))$ .

${((4 \cos (x) - 7 \sin (x)) (4 \cos (x) - 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.2

Expand $(4 \cos (x) - 7 \sin (x)) (4 \cos (x) - 7 \sin (x))$ using the FOIL Method.

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Step 2.1.2.1

Apply the distributive property.

${(4 \cos (x) (4 \cos (x) - 7 \sin (x)) - 7 \sin (x) (4 \cos (x) - 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.2.2

Apply the distributive property.

${(4 \cos (x) (4 \cos (x)) + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x) - 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.2.3

Apply the distributive property.

${(4 \cos (x) (4 \cos (x)) + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3

Simplify and combine like terms.

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Step 2.1.3.1

Simplify each term.

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Step 2.1.3.1.1

Multiply $4 \cos (x) (4 \cos (x))$ .

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Step 2.1.3.1.1.1

Multiply $4$ by $4$ .

${(16 \cos (x) \cos (x) + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.1.2

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

${(16 (\cos^{1} (x) \cos (x)) + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.1.3

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

${(16 (\cos^{1} (x) \cos^{1} (x)) + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.1.4

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

${(16 {\cos (x)}^{1 + 1} + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.1.5

Add $1$ and $1$ .

${(16 \cos^{2} (x) + 4 \cos (x) (- 7 \sin (x)) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.2

Multiply $- 7$ by $4$ .

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 7 \sin (x) (4 \cos (x)) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.3

Multiply $4$ by $- 7$ .

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \sin (x) \cos (x) - 7 \sin (x) (- 7 \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.4

Multiply $- 7 \sin (x) (- 7 \sin (x))$ .

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Step 2.1.3.1.4.1

Multiply $- 7$ by $- 7$ .

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \sin (x) \cos (x) + 49 \sin (x) \sin (x) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.4.2

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

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \sin (x) \cos (x) + 49 (\sin^{1} (x) \sin (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.4.3

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

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \sin (x) \cos (x) + 49 (\sin^{1} (x) \sin^{1} (x)) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.4.4

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

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \sin (x) \cos (x) + 49 {\sin (x)}^{1 + 1} + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.1.4.5

Add $1$ and $1$ .

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \sin (x) \cos (x) + 49 \sin^{2} (x) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.2

Reorder the factors of $- 28 \sin (x) \cos (x)$ .

${(16 \cos^{2} (x) - 28 \cos (x) \sin (x) - 28 \cos (x) \sin (x) + 49 \sin^{2} (x) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.3.3

Subtract $28 \cos (x) \sin (x)$ from $- 28 \cos (x) \sin (x)$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + {(7 \cos (x) + 4 \sin (x))}^{2})}^{2} = {(65)}^{2}$

Step 2.1.4

Rewrite ${(7 \cos (x) + 4 \sin (x))}^{2}$ as $(7 \cos (x) + 4 \sin (x)) (7 \cos (x) + 4 \sin (x))$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + (7 \cos (x) + 4 \sin (x)) (7 \cos (x) + 4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.5

Expand $(7 \cos (x) + 4 \sin (x)) (7 \cos (x) + 4 \sin (x))$ using the FOIL Method.

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Step 2.1.5.1

Apply the distributive property.

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 7 \cos (x) (7 \cos (x) + 4 \sin (x)) + 4 \sin (x) (7 \cos (x) + 4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.5.2

Apply the distributive property.

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 7 \cos (x) (7 \cos (x)) + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x) + 4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.5.3

Apply the distributive property.

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 7 \cos (x) (7 \cos (x)) + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6

Simplify and combine like terms.

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Step 2.1.6.1

Simplify each term.

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Step 2.1.6.1.1

Multiply $7 \cos (x) (7 \cos (x))$ .

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Step 2.1.6.1.1.1

Multiply $7$ by $7$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos (x) \cos (x) + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.1.2

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

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 (\cos^{1} (x) \cos (x)) + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.1.3

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

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 (\cos^{1} (x) \cos^{1} (x)) + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.1.4

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

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 {\cos (x)}^{1 + 1} + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.1.5

Add $1$ and $1$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 7 \cos (x) (4 \sin (x)) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.2

Multiply $4$ by $7$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 4 \sin (x) (7 \cos (x)) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.3

Multiply $7$ by $4$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \sin (x) \cos (x) + 4 \sin (x) (4 \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.4

Multiply $4 \sin (x) (4 \sin (x))$ .

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Step 2.1.6.1.4.1

Multiply $4$ by $4$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \sin (x) \cos (x) + 16 \sin (x) \sin (x))}^{2} = {(65)}^{2}$

Step 2.1.6.1.4.2

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

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \sin (x) \cos (x) + 16 (\sin^{1} (x) \sin (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.4.3

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

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \sin (x) \cos (x) + 16 (\sin^{1} (x) \sin^{1} (x)))}^{2} = {(65)}^{2}$

Step 2.1.6.1.4.4

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

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \sin (x) \cos (x) + 16 {\sin (x)}^{1 + 1})}^{2} = {(65)}^{2}$

Step 2.1.6.1.4.5

Add $1$ and $1$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \sin (x) \cos (x) + 16 \sin^{2} (x))}^{2} = {(65)}^{2}$

Step 2.1.6.2

Reorder the factors of $28 \sin (x) \cos (x)$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 28 \cos (x) \sin (x) + 28 \cos (x) \sin (x) + 16 \sin^{2} (x))}^{2} = {(65)}^{2}$

Step 2.1.6.3

Add $28 \cos (x) \sin (x)$ and $28 \cos (x) \sin (x)$ .

${(16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 56 \cos (x) \sin (x) + 16 \sin^{2} (x))}^{2} = {(65)}^{2}$

Step 2.2

Simplify terms.

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Step 2.2.1

Combine the opposite terms in $16 \cos^{2} (x) - 56 \cos (x) \sin (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 56 \cos (x) \sin (x) + 16 \sin^{2} (x)$ .

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Step 2.2.1.1

Add $- 56 \cos (x) \sin (x)$ and $56 \cos (x) \sin (x)$ .

${(16 \cos^{2} (x) + 0 + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 16 \sin^{2} (x))}^{2} = {(65)}^{2}$

Step 2.2.1.2

Add $16 \cos^{2} (x)$ and $0$ .

${(16 \cos^{2} (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x) + 16 \sin^{2} (x))}^{2} = {(65)}^{2}$

Step 2.2.2

Move $16 \sin^{2} (x)$ .

${(16 \cos^{2} (x) + 16 \sin^{2} (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.2.3

Factor $16$ out of $16 \cos^{2} (x)$ .

${(16 (\cos^{2} (x)) + 16 \sin^{2} (x) + 49 \sin^{2} (x) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.2.4

Factor $16$ out of $16 \sin^{2} (x)$ .

${(16 (\cos^{2} (x)) + 16 (\sin^{2} (x)) + 49 \sin^{2} (x) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.2.5

Factor $16$ out of $16 (\cos^{2} (x)) + 16 (\sin^{2} (x))$ .

${(16 (\cos^{2} (x) + \sin^{2} (x)) + 49 \sin^{2} (x) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.3

Rearrange terms.

${(16 (\sin^{2} (x) + \cos^{2} (x)) + 49 \sin^{2} (x) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.4

Apply pythagorean identity.

${(16 \cdot 1 + 49 \sin^{2} (x) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.5

Simplify with factoring out.

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Step 2.5.1

Factor $49$ out of $49 \sin^{2} (x)$ .

${(16 \cdot 1 + 49 (\sin^{2} (x)) + 49 \cos^{2} (x))}^{2} = {(65)}^{2}$

Step 2.5.2

Factor $49$ out of $49 \cos^{2} (x)$ .

${(16 \cdot 1 + 49 (\sin^{2} (x)) + 49 (\cos^{2} (x)))}^{2} = {(65)}^{2}$

Step 2.5.3

Factor $49$ out of $49 (\sin^{2} (x)) + 49 (\cos^{2} (x))$ .

${(16 \cdot 1 + 49 (\sin^{2} (x) + \cos^{2} (x)))}^{2} = {(65)}^{2}$

Step 2.6

Apply pythagorean identity.

${(16 \cdot 1 + 49 \cdot 1)}^{2} = {(65)}^{2}$

Step 2.7

Simplify terms.

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Step 2.7.1

Simplify each term.

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Step 2.7.1.1

Multiply $16$ by $1$ .

${(16 + 49 \cdot 1)}^{2} = {(65)}^{2}$

Step 2.7.1.2

Multiply $49$ by $1$ .

${(16 + 49)}^{2} = {(65)}^{2}$

Step 2.7.2

Simplify the expression.

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Step 2.7.2.1

Add $16$ and $49$ .

$65^{2} = {(65)}^{2}$

Step 2.7.2.2

Raise $65$ to the power of $2$ .

$4225 = {(65)}^{2}$

Step 3

Raise $65$ to the power of $2$ .

$4225 = 4225$

Step 4

Since $4225 = 4225$ , the equation will always be true for any value of $x$ .

All real numbers

Step 5

The result can be shown in multiple forms.

All real numbers

Interval Notation:

$(- \infty, \infty)$