How do I integrate 4x^2/(x^3-8) from 0 to 8

It is an improper integral and I know it diverges but I don't know why

i found u=x^3-8

but am getting stuck after that

How do I integrate 4x^2/(x^3-8) from 0 to 8

It is an improper integral and I know it diverges but I don't know why

i found u=x^3-8

but am getting stuck after that

Tutors, please sign in to answer this question.

Or you can use a u substitution that you tried.

We have u = x^{3} - 8, and du = 3x^{2}dx so

∫ [4x^{2}/(x^{3 }- 8)] dx = (4/3) ∫ du/u = (4/3) ln|u| + C = (4/3) ln|x^{3
}- 8| + C

from 0 to 8 it diverges since at x = 2 you get (4/3) ln 0 → ∞ as said by Robert.

You can tell it diverges even before doing the integral, because at x = 2, the denominator of 4x^{2}/(x^{3} - 8) is zero. There's a vertical asymptote at x = 2 (and that makes it difficult to find the area under the curve!).

Remember that that's the point of integration - to find the area under a curve, and you can't find the area under a vertical asymptote. Looking at a graph of the function may help to see this:

∫4x^2/(x^3-8) dx

= ∫(4/3)/(x^3-8) d(x^3-8)

= (4/3)ln|x^3-8|, which approaches infinity as x --> 2.

So, the integral diverges.

Ronniel M.

Making Math Easy- SAT Prep, Algebra, Precalculus, English, Spanish

Clifton, NJ

5.0
(158 ratings)

Sean B.

Premier NYC Math tutor - young, passionate and talented

New York, NY

4.8
(30 ratings)

Richard B.

Effective and Experienced Math and Science Tutor and Teacher

South Orange, NJ

5.0
(197 ratings)

## Comments

Wow thanks for your help

That actually makes sense