more derivatives....

Question

lovelyharmonics · Answer

f(x)=-4x^2+11x at x=10

neer2890 · Answer

just put 10 inplace of x.
find f(10)

lovelyharmonics · Answer

really? its that freaking simple?

anonymous · Answer

you have to differentiate it, right?

lovelyharmonics · Answer

differentiate what c:

lovelyharmonics · Answer

it just says find the derivative

anonymous · Answer

you said derivate on top

anonymous · Answer

uh huh

lovelyharmonics · Answer

no i didnt XD

anonymous · Answer

lovelyharmonics
more derivatives....

lovelyharmonics · Answer

yeah but i didnt say derivate...

lovelyharmonics · Answer

can you help :c

anonymous · Answer

so you are not supposed to take derivative of
f(x)=-4x^2+11x at x=10?

lovelyharmonics · Answer

/).(\ i dont know. my entire question is find the derivative...... insert equation here

anonymous · Answer

well
then find derivative of -4x^2+11x 
like the formula hartnn had told

kirbykirby · Answer

I'm assuming you find the derivative first, then plug in x = 10

anonymous · Answer

yep

lovelyharmonics · Answer

why cant it just be easy :c

kirbykirby · Answer

$f(x) = -4x^2+11x$
derivative:
$f'(x)=-4(2)x+11=-8x+11$
plug in x = 10:
$f'(10)=-8(10)+11=-80+11=-69$

lovelyharmonics · Answer

wait wheres the fractions.... its d/dx x^n

kirbykirby · Answer

$$ f'(x)=\frac{d}{dx}f(x)$$

lovelyharmonics · Answer

nuuuu.... it was $$\frac{ d }{ dx }x^n$$

kirbykirby · Answer

Is the question finding the derivative of $x^n$ or $-4x^2+11x$ ?

lovelyharmonics · Answer

find the derivative of f(x)=-4x^2+11x at x=10

kirbykirby · Answer

Well ok, that is the answer above that I wrote...

kirbykirby · Answer

maybe you're wondering how to use the power rule??
$$ \frac{d}{dx}x^n = nx^{n-1}$$

for $x^2$, $n=2$ so $$ \frac{d}{dx}x^2=2x^{2-1}=2x^1=2x$$

That is how I got from $-4x^2$ to $-4(2)x$... but of course, you ignore the coefficient -4 in front