# integration through substitutionWatch

#1
f(x)=(x^3) * (4+x^2)^(-1/2)

using u = 4 + x^2 as substitution.

I'm unable to identify which substitution [direct or reverse] to use.
0
7 years ago
#2
? It tells you the substitution to use
Find du/dx also to change the variable of the integral
0
#3
(Original post by Potassium^2)
? It tells you the substitution to use
Find du/dx also to change the variable of the integral
du/dx = 2x, problem is I can't fit it into the equation... [having already substituted u for x).
0
7 years ago
#4
Ah I see what you mean
have a look here: http://www.wolframalpha.com/input/?i...x%5E2%29%29%5D
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7 years ago
#5
(Original post by one-final-hit)
du/dx = 2x, problem is I can't fit it into the equation... [having already substituted u for x).
You can rewrite as .

0
7 years ago
#6
(Original post by one-final-hit)
du/dx = 2x, problem is I can't fit it into the equation... [having already substituted u for x).
Note that . If you consider the integral of this and use the substitution, it should be clear how this substitution can be fully applied to f(x).

EDIT: BJack is too fast.
0
#7
Cheers guys, I think I can take it from here
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