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# Do I have to expand when I use the chain rule? watch

1. Let's say I have to different y=3(4-x)^8

Is the answer 24(4-x)^7(-1)

Or do I have to expand this? Is this even correct?
2. expand?
3. (Original post by TeeEm)
expand?
the brackets?

So instead of 24(4-x)^7(-1)

I get (-96+24x)^7
4. your method is fine. you can join up the 24 and the -1, but leave the rest in brackets ?
5. (Original post by Dinasaurus)
the brackets?

So instead of 24(4-x)^7(-1)

I get (-96+24x)^7
that is incorrect !!
the bracket is "locked" to the power of 7
6. (Original post by TeeEm)
that is incorrect !!
the bracket is "locked" to the power of 7
So was it correct the first time round? Is it normal for chain rule answers to be so messy?
7. (Original post by Dinasaurus)
the brackets?

So instead of 24(4-x)^7(-1)

I get (-96+24x)^7
(-96+24x)^7 is not the same as 24(4-x)^7(-1), you'd have to use the binomial expansion to expand the (4-x)^7 term. With these questions, it's always best to just leave it as it is, except multiply the (-1) and (24) together. It's correct, by the way :P
8. (Original post by Dinasaurus)
So was it correct the first time round? Is it normal for chain rule answers to be so messy?
it was fine.

(they are not messy)

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