What is the integral of-cos(x)sin(2x) ?

The integral of-cos(x)sin(2x) is 2/3 cos^3(x)+C

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integral of-cos(x)sin(2x)

\int - cos (x) sin (2 x) d x

\frac{2}{3} cos^{3} (x) + C

Solution steps

\int - cos (x) sin (2 x) d x

Take the constant out:

\int a \cdot f (x) d x = a \cdot \int f (x) d x

= - \int cos (x) sin (2 x) d x

Rewrite using trig identities

= - \int 2 cos^{2} (x) sin (x) d x

Take the constant out:

\int a \cdot f (x) d x = a \cdot \int f (x) d x

= - 2 \cdot \int cos^{2} (x) sin (x) d x

Apply u-substitution

= - 2 \cdot \int - u^{2} d u

Take the constant out:

\int a \cdot f (x) d x = a \cdot \int f (x) d x

= - 2 (- \int u^{2} d u)

Apply the Power Rule

= - 2 (- \frac{u ^{3}}{3})

Substitute back

u = cos (x)

= - 2 (- \frac{cos ^{3} ( x )}{3})

Simplify

- 2 (- \frac{cos ^{3} ( x )}{3}) : \frac{2}{3} cos^{3} (x)

= \frac{2}{3} cos^{3} (x)

Add a constant to the solution

= \frac{2}{3} cos^{3} (x) + C

What is the integral of-cos(x)sin(2x) ?
The integral of-cos(x)sin(2x) is 2/3 cos^3(x)+C