# Integral - help needed please

1. Jan 28, 2006

### Natasha1

I have been asked to state which one of the following 3 integrals I can solve using integration by substitution

(i) integral cos (x^2) dx

(ii) integral x cos x (x^2) dx

(iii) integral x^2 cos (x^2) dx

I would say that it is (ii) because x is the derivative of x^2 is that the correct answer or is there anything else I should add? Thanks in advance

2. Jan 28, 2006

### arildno

That would be okay enough, I guess.

3. Jan 28, 2006

### Jameson

Well, x isn't the derivative of $x^2$, but I know what you meant. Maybe you could also show how basic substitution fails on the other two.

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