Mathematics
6 Online
OpenStudy (math2400):
antiderivative problem
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OpenStudy (math2400):
OpenStudy (adi3):
does F'(0) means that f wont be included in the sum
OpenStudy (math2400):
i'm not sure....
OpenStudy (adi3):
@butterflydreamer
OpenStudy (xapproachesinfinity):
well first find f' from f''
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OpenStudy (math2400):
can u show me how?
OpenStudy (math2400):
please :)
OpenStudy (xapproachesinfinity):
\[f''(x)=6x+6\sin x \Longrightarrow \int 6x+6\sin x dx=f'(x) \\ 3x^2-6\cos x+c=f'(x) \]
OpenStudy (math2400):
so i do the anti derive. again?
OpenStudy (xapproachesinfinity):
through the givens we can find c
f'(0)=3(0)-6cos0+c=3
-6+c=3
c=9
so \[f'(x)=3x^2-6\cos x+9\]
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OpenStudy (math2400):
ok
OpenStudy (xapproachesinfinity):
yes you have to apply the anti derive one more time to get to f
OpenStudy (math2400):
so i got x^3 - 6sinx
OpenStudy (math2400):
then i'd need the c I'm guessing?
OpenStudy (xapproachesinfinity):
x^3-6sinx +c
then find the c again
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OpenStudy (xapproachesinfinity):
yah you are given that f(0)=3
OpenStudy (math2400):
it it 9 then?
OpenStudy (math2400):
wait no
OpenStudy (xapproachesinfinity):
no solve don't just guess!
OpenStudy (math2400):
3
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OpenStudy (math2400):
cuz u plug in zero into the equation and then set it equal to 3?
OpenStudy (xapproachesinfinity):
yes
OpenStudy (xapproachesinfinity):
exactly!
OpenStudy (freckles):
well ...
OpenStudy (freckles):
I think someone forgot to integrate 9 earlier
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OpenStudy (freckles):
what did you get for f(x)
given \[f'(x)=3x^2-6\cos x+9\]
OpenStudy (math2400):
i got x^3 - 6sinx
OpenStudy (freckles):
why ignore the 9?
OpenStudy (math2400):
oppss
OpenStudy (math2400):
got it thanks!!
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OpenStudy (freckles):
recall (9x+d)'=(9x)'+(d)'=9+0=9
so you get f(x)= x^3-6sin(x)+9x+d
then you find the constant d using f(0)=3
OpenStudy (xapproachesinfinity):
eh i forgot the constant 9 too :)
got catch @freckles
OpenStudy (freckles):
My kitty told me about it.
OpenStudy (xapproachesinfinity):
good catch i mean :)
kitty haha