What is the integral of cos^3(x/3) ?

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

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integral of cos^3(x/3)

\int cos^{3} (\frac{x}{3}) d x

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

Solution steps

\int cos^{3} (\frac{x}{3}) d x

Apply u-substitution

: \int cos^{3} (u) \cdot 3 d u

= \int cos^{3} (u) \cdot 3 d u

Take the constant out:

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

= 3 \cdot \int cos^{3} (u) d u

Rewrite using trig identities

= 3 \cdot \int (1 - sin^{2} (u)) cos (u) d u

Apply u-substitution

: \int 1 - v^{2} d v

= 3 \cdot \int 1 - v^{2} d v

Apply the Sum Rule:

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

= 3 (\int 1 d v - \int v^{2} d v)

\int 1 d v = v

\int v^{2} d v = \frac{v ^{3}}{3}

= 3 (v - \frac{v ^{3}}{3})

Substitute back

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

Simplify

3 (sin (\frac{x}{3}) - \frac{sin ^{3} ( \frac{x}{3} )}{3}) : 3 sin (\frac{x}{3}) - sin^{3} (\frac{x}{3})

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

Add a constant to the solution

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

y = x + 2, y = \frac{1}{x + 1}, x = 0, x = 2

\frac{d y}{d t} = y^{1.01}

\int \frac{ln ( x )}{x ^{1.2}} d x

x \to - 1 lim (2 x + 2)

\int sin (x) \cdot ln (cos (x)) d x

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