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

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

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integral of sin(x)sin(2x)

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

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

Solution steps

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

Rewrite using trig identities

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

Take the constant out:

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

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

Apply u-substitution

: \int u^{2} d u

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

Apply the Power Rule

: \frac{u ^{3}}{3}

= 2 \cdot \frac{u ^{3}}{3}

Substitute back

u = sin (x)

= 2 \cdot \frac{sin ^{3} ( x )}{3}

Simplify

2 \cdot \frac{sin ^{3} ( x )}{3} : \frac{2}{3} sin^{3} (x)

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

Add a constant to the solution

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

y^{^{'}} = 4 x + y, y (0) = 1

\int_{0}^{6} 6 x - (3 x - 12) d x

\int_{0}^{\infty} \frac{1}{7 + x} d x

\int e^{2} x d x

(e^{x} + e^{- x}) y^{^{'}} = y^{2}

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