What is the integral of sin(3x)sin(nx) ?

The integral of sin(3x)sin(nx) is 1/2 (-1/(3+n)sin(3x+nx)+1/(3-n)sin(3x-nx))+C

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integral of sin(3x)sin(nx)

\int sin (3 x) sin (n x) d x

\frac{1}{2} (- \frac{1}{3 + n} sin (3 x + n x) + \frac{1}{3 - n} sin (3 x - n x)) + C

Solution steps

\int sin (3 x) sin (n x) d x

Rewrite using trig identities

= \int \frac{- cos ( 3 x + n x ) + cos ( 3 x - n x )}{2} d x

Take the constant out:

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

= \frac{1}{2} \cdot \int - cos (3 x + n x) + cos (3 x - n x) d x

Apply the Sum Rule:

\int f (x) \pm g (x) d x = \int f (x) d x \pm \int g (x) d x

= \frac{1}{2} (- \int cos (3 x + n x) d x + \int cos (3 x - n x) d x)

\int cos (3 x + n x) d x = \frac{1}{3 + n} sin (3 x + n x)

\int cos (3 x - n x) d x = \frac{1}{3 - n} sin (3 x - n x)

= \frac{1}{2} (- \frac{1}{3 + n} sin (3 x + n x) + \frac{1}{3 - n} sin (3 x - n x))

Add a constant to the solution

= \frac{1}{2} (- \frac{1}{3 + n} sin (3 x + n x) + \frac{1}{3 - n} sin (3 x - n x)) + C

(1 - t) (3 + t^{2})^{- 1}

y = \frac{sin ( x )}{x}

\frac{x + 5}{x - 5}

y^{^{'}} = 5 x + y

\int x 9 x^{2} + 4 d x

What is the integral of sin(3x)sin(nx) ?
The integral of sin(3x)sin(nx) is 1/2 (-1/(3+n)sin(3x+nx)+1/(3-n)sin(3x-nx))+C