Question:

Find the integrals of the function: \(sin^3 x\, cos^3 x\)

Updated On: Oct 19, 2023
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Solution and Explanation

The correct answer is: \(= \frac{cos^6x}{6}-\frac{cos^4x}{4}+C\)
Let \(I = ∫sin^3 x\, cos^3 x.dx\)
\(= ∫cos^3 x. sin^2 x. sin x. dx\)
\(= ∫cos^3 x(1-cos^2 x)sin x.dx\)
Let \(cos x = 1\)
\(⇒ -sin x.dx = dt\)
\(⇒ I = - ∫t^3(1-t^2)dt\)
\(= -∫(t^3-t^5)dt\)
\(= -[{\frac{t^4}{4}-\frac{t^6}{6}}]+C\)
\(= - [{\frac{cos^4x}{4}-\frac{cos^6x}{6}}]+C\)
\(= \frac{cos^6x}{6}-\frac{cos^4x}{4}+C\)
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Concepts Used:

Methods of Integration

Given below is the list of the different methods of integration that are useful in simplifying integration problems:

Integration by Parts:

 If f(x) and g(x) are two functions and their product is to be integrated, then the formula to integrate f(x).g(x) using by parts method is:

∫f(x).g(x) dx = f(x) ∫g(x) dx − ∫(f′(x) [ ∫g(x) dx)]dx + C

Here f(x) is the first function and g(x) is the second function.

Method of Integration Using Partial Fractions:

The formula to integrate rational functions of the form f(x)/g(x) is:

∫[f(x)/g(x)]dx = ∫[p(x)/q(x)]dx + ∫[r(x)/s(x)]dx

where

f(x)/g(x) = p(x)/q(x) + r(x)/s(x) and

g(x) = q(x).s(x)

Integration by Substitution Method

Hence the formula for integration using the substitution method becomes:

∫g(f(x)) dx = ∫g(u)/h(u) du

Integration by Decomposition

Reverse Chain Rule

This method of integration is used when the integration is of the form ∫g'(f(x)) f'(x) dx. In this case, the integral is given by,

∫g'(f(x)) f'(x) dx = g(f(x)) + C

Integration Using Trigonometric Identities