Asked by Ann

Evaluate ∫(2x^3/√(1-x^4))dx

I can't figure out what u and du is...

please help thanks
Answered by bobpursley
u= sqrt(1-x^4)

du= 1/2sqrt(1-x^4)*(-4x^3)dx

= -2x^3/sqrt(1-x^4) dx

so the integral is
INT -1/u du
Answered by Steve
or,
u = 1-x^4
du = -4x^3 du

so
∫(2x^3/√(1-x^4))dx
= -1/2 ∫1/√u du
= (-1/2)(2√u)
= -√(1-x^4)

Extra credit: Can you find the error in bobpursley's solution?
Answered by Ann
no, but thanks for your answer!
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