What is the integral of cos^2(9x) ?

The integral of cos^2(9x) is 1/2 (x+1/18 sin(18x))+C

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integral of cos^2(9x)

\int cos^{2} (9 x) d x

\frac{1}{2} (x + \frac{1}{18} sin (18 x)) + C

Solution steps

\int cos^{2} (9 x) d x

Rewrite using trig identities

= \int \frac{1}{2} (1 + cos (18 x)) 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 1 + cos (18 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 1 d x + \int cos (18 x) d x)

\int 1 d x = x

\int cos (18 x) d x = \frac{1}{18} sin (18 x)

= \frac{1}{2} (x + \frac{1}{18} sin (18 x))

Add a constant to the solution

= \frac{1}{2} (x + \frac{1}{18} sin (18 x)) + C

What is the integral of cos^2(9x) ?
The integral of cos^2(9x) is 1/2 (x+1/18 sin(18x))+C