Solve for x (5cos(x)-3sin(x))^2+16sin(x)^2=25

${(5 \cos (x) - 3 \sin (x))}^{2} + 16 \sin^{2} (x) = 25$

Step 1

Subtract $25$ from both sides of the equation.

${(5 \cos (x) - 3 \sin (x))}^{2} + 16 \sin^{2} (x) - 25 = 0$

Step 2

Simplify ${(5 \cos (x) - 3 \sin (x))}^{2} + 16 \sin^{2} (x) - 25$ .

Simplify each term.

Rewrite ${(5 \cos (x) - 3 \sin (x))}^{2}$ as $(5 \cos (x) - 3 \sin (x)) (5 \cos (x) - 3 \sin (x))$ .

$(5 \cos (x) - 3 \sin (x)) (5 \cos (x) - 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Expand $(5 \cos (x) - 3 \sin (x)) (5 \cos (x) - 3 \sin (x))$ using the FOIL Method.

Apply the distributive property.

$5 \cos (x) (5 \cos (x) - 3 \sin (x)) - 3 \sin (x) (5 \cos (x) - 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Apply the distributive property.

$5 \cos (x) (5 \cos (x)) + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x) - 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Apply the distributive property.

$5 \cos (x) (5 \cos (x)) + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Simplify and combine like terms.

Simplify each term.

Multiply $5 \cos (x) (5 \cos (x))$ .

Multiply $5$ by $5$ .

$25 \cos (x) \cos (x) + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

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

$25 (\cos^{1} (x) \cos (x)) + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

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

$25 (\cos^{1} (x) \cos^{1} (x)) + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

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

$25 {\cos (x)}^{1 + 1} + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Add $1$ and $1$ .

$25 \cos^{2} (x) + 5 \cos (x) (- 3 \sin (x)) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Multiply $- 3$ by $5$ .

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 3 \sin (x) (5 \cos (x)) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Multiply $5$ by $- 3$ .

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \sin (x) \cos (x) - 3 \sin (x) (- 3 \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

Multiply $- 3 \sin (x) (- 3 \sin (x))$ .

Multiply $- 3$ by $- 3$ .

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \sin (x) \cos (x) + 9 \sin (x) \sin (x) + 16 \sin^{2} (x) - 25 = 0$

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

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \sin (x) \cos (x) + 9 (\sin^{1} (x) \sin (x)) + 16 \sin^{2} (x) - 25 = 0$

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

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \sin (x) \cos (x) + 9 (\sin^{1} (x) \sin^{1} (x)) + 16 \sin^{2} (x) - 25 = 0$

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

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \sin (x) \cos (x) + 9 {\sin (x)}^{1 + 1} + 16 \sin^{2} (x) - 25 = 0$

Add $1$ and $1$ .

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \sin (x) \cos (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) - 25 = 0$

Reorder the factors of $- 15 \sin (x) \cos (x)$ .

$25 \cos^{2} (x) - 15 \cos (x) \sin (x) - 15 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) - 25 = 0$

Subtract $15 \cos (x) \sin (x)$ from $- 15 \cos (x) \sin (x)$ .

$25 \cos^{2} (x) - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) - 25 = 0$

Move $- 25$ .

$25 \cos^{2} (x) - 25 - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Reorder $25 \cos^{2} (x)$ and $- 25$ .

$- 25 + 25 \cos^{2} (x) - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Factor $- 25$ out of $- 25$ .

$- 25 (1) + 25 \cos^{2} (x) - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Factor $- 25$ out of $25 \cos^{2} (x)$ .

$- 25 (1) - 25 (- \cos^{2} (x)) - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Factor $- 25$ out of $- 25 (1) - 25 (- \cos^{2} (x))$ .

$- 25 (1 - \cos^{2} (x)) - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Apply pythagorean identity.

$- 25 \sin^{2} (x) - 30 \cos (x) \sin (x) + 9 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Add $- 25 \sin^{2} (x)$ and $9 \sin^{2} (x)$ .

$- 30 \cos (x) \sin (x) - 16 \sin^{2} (x) + 16 \sin^{2} (x) = 0$

Combine the opposite terms in $- 30 \cos (x) \sin (x) - 16 \sin^{2} (x) + 16 \sin^{2} (x)$ .

Add $- 16 \sin^{2} (x)$ and $16 \sin^{2} (x)$ .

$- 30 \cos (x) \sin (x) + 0 = 0$

Add $- 30 \cos (x) \sin (x)$ and $0$ .

$- 30 \cos (x) \sin (x) = 0$

Step 3

If any individual factor on the left side of the equation is equal to $0$ , the entire expression will be equal to $0$ .

$\cos (x) = 0$

$\sin (x) = 0$

Step 4

Set $\cos (x)$ equal to $0$ and solve for $x$ .

Set $\cos (x)$ equal to $0$ .

$\cos (x) = 0$

Solve $\cos (x) = 0$ for $x$ .

Take the inverse cosine of both sides of the equation to extract $x$ from inside the cosine.

$x = \arccos (0)$

Simplify the right side.

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

$x = \frac{π}{2}$

The cosine function is positive in the first and fourth quadrants. To find the second solution, subtract the reference angle from $2 π$ to find the solution in the fourth quadrant.

$x = 2 π - \frac{π}{2}$

Simplify $2 π - \frac{π}{2}$ .

To write $2 π$ as a fraction with a common denominator, multiply by $\frac{2}{2}$ .

$x = 2 π \cdot \frac{2}{2} - \frac{π}{2}$

Combine fractions.

Combine $2 π$ and $\frac{2}{2}$ .

$x = \frac{2 π \cdot 2}{2} - \frac{π}{2}$

Combine the numerators over the common denominator.

$x = \frac{2 π \cdot 2 - π}{2}$

Simplify the numerator.

Multiply $2$ by $2$ .

$x = \frac{4 π - π}{2}$

Subtract $π$ from $4 π$ .

$x = \frac{3 π}{2}$

Find the period of $\cos (x)$ .

The period of the function can be calculated using $\frac{2 π}{| b |}$ .

$\frac{2 π}{| b |}$

Replace $b$ with $1$ in the formula for period.

$\frac{2 π}{| 1 |}$

The absolute value is the distance between a number and zero. The distance between $0$ and $1$ is $1$ .

$\frac{2 π}{1}$

Divide $2 π$ by $1$ .

$2 π$

The period of the $\cos (x)$ function is $2 π$ so values will repeat every $2 π$ radians in both directions.

$x = \frac{π}{2} + 2 π n, \frac{3 π}{2} + 2 π n$ , for any integer $n$

Step 5

Set $\sin (x)$ equal to $0$ and solve for $x$ .

Set $\sin (x)$ equal to $0$ .

$\sin (x) = 0$

Solve $\sin (x) = 0$ for $x$ .

Take the inverse sine of both sides of the equation to extract $x$ from inside the sine.

$x = \arcsin (0)$

Simplify the right side.

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

$x = 0$

The sine function is positive in the first and second quadrants. To find the second solution, subtract the reference angle from $π$ to find the solution in the second quadrant.

$x = π - 0$

Subtract $0$ from $π$ .

$x = π$

Find the period of $\sin (x)$ .

The period of the function can be calculated using $\frac{2 π}{| b |}$ .

$\frac{2 π}{| b |}$

Replace $b$ with $1$ in the formula for period.

$\frac{2 π}{| 1 |}$

The absolute value is the distance between a number and zero. The distance between $0$ and $1$ is $1$ .

$\frac{2 π}{1}$

Divide $2 π$ by $1$ .

$2 π$

The period of the $\sin (x)$ function is $2 π$ so values will repeat every $2 π$ radians in both directions.

$x = 2 π n, π + 2 π n$ , for any integer $n$

Step 6

The final solution is all the values that make $- 30 \cos (x) \sin (x) = 0$ true.

$x = \frac{π}{2} + 2 π n, \frac{3 π}{2} + 2 π n, 2 π n, π + 2 π n$ , for any integer $n$

Step 7

Consolidate the answers.

$x = \frac{π n}{2}$ , for any integer $n$

Solve for x (5cos(x)-3sin(x))^2+16sin(x)^2=25

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