What is the integral from 0 to pi/2 of sin(x)sin(2x) ?

The integral from 0 to pi/2 of sin(x)sin(2x) is 2/3

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integral from 0 to pi/2 of sin(x)sin(2x)

\int_{0}^{\frac{π}{2}} sin (x) sin (2 x) d x

\frac{2}{3}

Decimal

0.66666 \dots

Solution steps

\int_{0}^{\frac{π}{2}} sin (x) sin (2 x) d x

Rewrite using trig identities

= \int_{0}^{\frac{π}{2}} 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_{0}^{\frac{π}{2}} sin^{2} (x) cos (x) d x

Apply u-substitution

= 2 \cdot \int_{0}^{1} u^{2} d u

Apply the Power Rule

= 2 [\frac{u ^{3}}{3}]_{0}^{1}

Compute the boundaries:

\frac{1}{3}

= 2 \cdot \frac{1}{3}

Simplify

= \frac{2}{3}

What is the integral from 0 to pi/2 of sin(x)sin(2x) ?
The integral from 0 to pi/2 of sin(x)sin(2x) is 2/3