What is the integral of (21)/(1+9x^2) ?

The integral of (21)/(1+9x^2) is 7arctan(3x)+C

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integral of (21)/(1+9x^2)

\int \frac{21}{1 + 9 x ^{2}} d x

7 arctan (3 x) + C

Solution steps

\int \frac{21}{1 + 9 x ^{2}} d x

Take the constant out:

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

= 21 \cdot \int \frac{1}{1 + 9 x ^{2}} d x

Apply Integral Substitution

= 21 \cdot \int \frac{1}{3 ( 1 + u ^{2} )} d u

Take the constant out:

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

= 21 \cdot \frac{1}{3} \cdot \int \frac{1}{1 + u ^{2}} d u

Use the common integral:

\int \frac{1}{1 + u ^{2}} d u = arctan (u)

= 21 \cdot \frac{1}{3} arctan (u)

Substitute back

u = 3 x

= 21 \cdot \frac{1}{3} arctan (3 x)

Simplify

21 \cdot \frac{1}{3} arctan (3 x) : 7 arctan (3 x)

= 7 arctan (3 x)

Add a constant to the solution

= 7 arctan (3 x) + C

What is the integral of (21)/(1+9x^2) ?
The integral of (21)/(1+9x^2) is 7arctan(3x)+C