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Brad's questions at Yahoo! Answers regarding finding anti-derivatives

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MarkFL

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Feb 24, 2012
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Here are the questions:

Find the antiderivative?


Struggling with these two antiderivative:

-8(4x-1)^1/2

-2(3x^4-5)^2

Please explain how you worked them out with full working
I have posted a link there to this topic so the OP can see my work.
 
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MarkFL

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Feb 24, 2012
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Re: Brad's questions at Yahoo Answers regarding finding anti-derivatives

Hello Brad,

1.) \(\displaystyle I=\int-8(4x-1)^{\frac{1}{2}}\,dx\)

Let's use the substitution:

\(\displaystyle u=4x-1\,\therefore\,du=4\,dx\)

And we may now state:

\(\displaystyle I=-2\int u^{\frac{1}{2}}\,du\)

Using the power rule for integration, we may write:

\(\displaystyle I=-2\left(\frac{u^{\frac{3}{2}}}{\frac{3}{2}} \right)+C=-\frac{4}{3}u^{\frac{3}{2}}+C\)

Back-substituting for $u$, there results:

\(\displaystyle I=-\frac{4}{3}(4x-1)^{\frac{3}{2}}+C\)

2.) \(\displaystyle I=\int -2(3x^4-5)^2\,dx\)

Bringing the constant factor in the integrand out front and expanding the binomial, we have:

\(\displaystyle I=-2\int 9x^8-30x^4+25\,dx\)

Applying the power rule term by term, we find:

\(\displaystyle I=-2\left(9\frac{x^9}{9}-30\frac{x^5}{5}+25x \right)+C\)

\(\displaystyle I=-2\left(x^9-6x^5+25x \right)+C\)