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# C4 Integration

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1. Please can someone help me?
In the Edexcel C4 Book, Exercise 6F Q3a I can't seem to understand why we have to substitute u^2 = x+4 instead of u=x+4
Any help would be great thanks
2. can you post the whole question please
3. You can substitute either u^2 = x+4 or u= x+4.
I did this exercise last night using u= x+4 and it worked.
However for some questions such as Q3 c, the substitution they offer is generally the best and easiest option to integrate.
4. (Original post by Cloudmc)
You can substitute either u^2 = x+4 or u= x+4.
I did this exercise last night using u= x+4 and it worked.
However for some questions such as Q3 c, the substitution they offer is generally the best and easiest option to integrate.
Oh I see, thank you. I must've made a mistake because I used u=x+4 but didn't get the right answer.
5. (Original post by Miffy98)
Oh I see, thank you. I must've made a mistake because I used u=x+4 but didn't get the right answer.

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