#1
Hey the question is out of a trial hsc paper:


The graph of y=f(x) passes through the point (2.12) and f'(x)=9x^2 + 4. Find f(x).


I think you need to use a formual with k in it but i forget what it is and i forgot my textbook at skool lol. A cookie for whoever can help Thanks.
#3
so f '(x) passes through (2,12) as well? find f(x)?

integrate f '(x)
f(x) = 3x^3 +4x +c

then plug in the x value (2) and the y value (12)

12 = 3(2)^3 + 4(2) + c

c =-20? i did this in my head sorry

now pug -20 back in for the integral constant and you have your f(x).

(goes to sleep)
Last edited by LawnDwarf at Jul 24, 2008,
#5
Integrate f'(x), then use the given coordinate to work out the value of c (the constant term)
EDIT: Beaten to it
Last edited by National_Anthem at Jul 24, 2008,
#6
ok, integrating f'(x) gives you:

y = 3x^3 + 4x + c.

Now, you have the point (2,12), so sub to find c.

12 = 3*8 + 4*2 + c

So

12 = 32 + c

c = -20

Hence, f(x) = 3x^3 + 4x - 20.

I think thats it, anyhoo.
#8
Quote by Ravenwoods
Hey the question is out of a trial hsc paper:


The graph of y=f(x) passes through the point (2.12) and f'(x)=9x^2 + 4. Find f(x).


I think you need to use a formual with k in it but i forget what it is and i forgot my textbook at skool lol. A cookie for whoever can help Thanks.


FOUND IT!!! not only once but twice!!
Quote by Spoony_Bard
Dude I got these strings the other day that couldn't be tuned to higher than 4 octaves below middle C then I realized that they were shoelaces and they weren't making any sound at all.
#9
Quote by Winsbury
isn't that f(x)?
i dont do advanced maths yet though, ive only just left school, so i could be wrong...


It could be f'(x) or f(x), but they have stated that it is f'(x) in this case.

Quote by LawnDwarf
so f '(x) passes through (2,12) as well? find f(x)?

integrate f '(x)
f(x) = 3x^3 +4x +c

then plug in the x value (2) and the y value (12)

12 = 3(2)^3 + 4(2) + c

c =20? i did this in my head sorry

now pug 20 back in for the integral constant and you have your f(x).

(goes to sleep)


...and this is right.
#10
ohh ok i got confused by the question lol thanks to all who helped, i can be at ease ... until i find another question i cant do ...
#11
Quote by gunners fan
FOUND IT!!! not only once but twice!!


Fail, f'(x) is not f(x).

DON'T MAKE ME DESTROY YOU!


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TURN OFF YOUR MIND RELAX AND FLOAT DOWNSTREAM

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