Math  /  Calculus

QuestionFind the indefinite integral. (Use CC for the constant of integration.) 981(x+9)2dx\int \frac{9}{\sqrt{81-(x+9)^{2}}} d x

Studdy Solution

STEP 1

1. We are given the integral 981(x+9)2dx\int \frac{9}{\sqrt{81-(x+9)^{2}}} \, dx.
2. We need to find the indefinite integral and include the constant of integration CC.

STEP 2

1. Recognize the form of the integral.
2. Use a trigonometric substitution to simplify the integral.
3. Simplify the expression using the substitution.
4. Integrate the simplified expression.
5. Substitute back to the original variable.
6. Include the constant of integration.

STEP 3

Recognize that the integral is of the form aa2u2du\int \frac{a}{\sqrt{a^2 - u^2}} \, du, which is related to the arcsine function.

STEP 4

Use the substitution u=x+9 u = x + 9 , then du=dx du = dx .
The integral becomes:
981u2du \int \frac{9}{\sqrt{81 - u^2}} \, du

STEP 5

Recognize that 81=92 81 = 9^2 , so the integral becomes:
992u2du \int \frac{9}{\sqrt{9^2 - u^2}} \, du
This is in the standard form for the arcsine function.

STEP 6

The integral 1a2u2du\int \frac{1}{\sqrt{a^2 - u^2}} \, du is arcsin(ua)+C\arcsin\left(\frac{u}{a}\right) + C.
Thus, our integral becomes:
9arcsin(u9)+C 9 \cdot \arcsin\left(\frac{u}{9}\right) + C

STEP 7

Substitute back u=x+9 u = x + 9 :
9arcsin(x+99)+C 9 \cdot \arcsin\left(\frac{x + 9}{9}\right) + C

STEP 8

Include the constant of integration CC.
The indefinite integral is:
9arcsin(x+99)+C \boxed{9 \arcsin\left(\frac{x + 9}{9}\right) + C}

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