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Hi,
I was wondering if someone could tell me if I have done this question right?
∫ xe^-4x² dx
OK I made u=4x² to get du=8x and rewrite as xdx=1/8du. I am not sure if i should have made these negative or not so I went with not.
The answer I got is -1/32 e^-4x² + c.
I am just not sure about the negative thing and if I have intergated the e part right.
I would be grateful for any help.
Thanks
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The correct answer is
Checking integration answers is very easy just differentiate your answer and see if you get the original expression back.
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Hi JaneFairfax,
Thanks for your help and tip I keep forgetting about differentiating to see if I have the right anwser.
Can I just double check something though when you integrate someting like e^4x the answer comes out as 1/4 e^4x + C so I was wondering why this did not happen in this question? This is where I got the -1/32 e^-4x² + c answer, or does this only happen if the question is not a change of variable?
Thanks again for your help
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After changing your variables, your integral became ∫1/8e^-udu.
There wasn't any coefficient in the power of e any more, so you only needed to divide by -1, not -4.
Why did the vector cross the road?
It wanted to be normal.
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Hi Mathsyperson,
Thanks for your help, I knew it would be something I was overlooking or looking to hard at
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