Solving Integrals using Substitution | Cosine Functions | Integral Help Needed

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SUMMARY

The discussion centers on solving integrals using integration by substitution, specifically focusing on three integrals involving cosine functions. The integral that can be solved using substitution is identified as (ii) integral x cos(x^2) dx, due to the relationship between x and its derivative x^2. The participants clarify that while the initial reasoning was incorrect, the concept of substitution is correctly applied in this case. Additionally, the discussion highlights that basic substitution does not work for the other two integrals.

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Natasha1
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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
 
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That would be okay enough, I guess.
 
Well, x isn't the derivative of [itex]x^2[/itex], but I know what you meant. Maybe you could also show how basic substitution fails on the other two.
 

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