grave maple
I don't understand what I did wrong i got 3/4 as an answer and the answer model got -3. they divided by
x^2 first and then filled in x = pi/2, i just can't see why what i did is "wrong" (filling in x = pi and then factoring out 4 pi squared). Someone help please.
Oh it's question 9b by the way
woeful caveBOT
I don't understand what I did wrong i got 3/4 as an answer and the answer model ...
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rigid moss
I don't understand what I did wrong i got 3/4 as an answer and the answer model ...
I think you did your factorization wrong
(-4)^k doesn't become 4 (-1)^k, but 4^k (-1)^k
Here it would be more practical to rewrite the sum as:
$$f'(x) = x^2 \sum_{k=0}^{\infty} (-1)^k \frac{2k+3}{(2k)!} \left( 2x\right)^{2k}$$
wheat bisonBOT
Miguel
grave maple
(-4)^k doesn't become 4 (-1)^k, but 4^k (-1)^k
oh my god that's so right!!
I was wondering where that 4 went in the answer model
still am actually. where did it go?
rigid moss
still am actually. where did it go?
It did not go anywhere
see that (2x)^2k I wrote?
they just replaced the 2x with pi
in other words they subbed x = pi/2
grave maple
wow they skipped so many steps inbetween hahahah thank you!
rigid moss
wow they skipped so many steps inbetween hahahah thank you!
No problem, hope it's clear now
humble jacinthBOT
@grave maple