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# Stationary Points C3 watch

1. I am really not sure what i am doing wrong.
Find the x co-ordinates of the stationary points of y=xln(x)
So I started differentiating:

dy =x* 1/x
dx

Which gives 1?
Then normally you put it equal to 0. 1=0?!

Thanks for any help
2. (Original post by shimmyjimmy)
I am really not sure what i am doing wrong.
Find the x co-ordinates of the stationary points of y=xln(x)
So I started differentiating:

dy =x* 1/x
dx

Which gives 1?
Then normally you put it equal to 0. 1=0?!

Thanks for any help
you've used the chain rule instead of the product rule
the answer is lnx + 1

as it's 1*lnx + x*1/x
= lnx + 1

edit: typo
3. Cheers guys, you are awesome. Just out of curiosity when you integrate say 4/x, you do get 4ln(x)(+k). So here you dont need to use product rule to get back to 4/x. Why is it different for xln(x)? Is it because its being multiplied by x?
Cheers
4. (Original post by shimmyjimmy)
Cheers guys, you are awesome. Just out of curiosity when you integrate say 4/x, you do get 4ln(x)(+k). So here you dont need to use product rule to get back to 4/x. Why is it different for xln(x)? Is it because its being multiplied by x?
Cheers
when you differentiate x, you get 1, which is fine, but 4 gives 0 as a differential.

in answer to your question, the 4 disappears, it's just ln|x| + c

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