Find f '(−5), if f(x) = (−4x2 − 2x)(−x2 − 9). Round your answer to the nearest integer. Use the hyphen symbol, -, for negative values.

Question

fibonaccichick666 · Answer

so, what do you think? what have you tried?

aryana_maria2323 · Answer

@DanJS

aryana_maria2323 · Answer

I don't know. I don't even know the first step to solve this problem.

fibonaccichick666 · Answer

$$Find~f '(−5), if~~~~~ f(x) = (−4x^2 − 2x)(−x^2 − 9)$$  Thats the eq, right?

fibonaccichick666 · Answer

so, what's the derivative of f(x)?

aryana_maria2323 · Answer

yes

aryana_maria2323 · Answer

The derivative is 16x^3+6x^2+72x+18

fibonaccichick666 · Answer

ok, so, derivatives.  Do you know how to find them?

fibonaccichick666 · Answer

lemme check that,  did you use the product rule?

aryana_maria2323 · Answer

yes I did

fibonaccichick666 · Answer

f '(−5), if f(x) = (−4x2 − 2x)(−x2 − 9)
$f'(x)= (-8x-2)(-x^2-9)+-2x(-4x^2-2x)  $

fibonaccichick666 · Answer

and you got that before simplifying?  I'll trust your algebra in that case

fibonaccichick666 · Answer

so now, you just need to find y' when x= -5

aryana_maria2323 · Answer

After replacing -5 for x I got -2192

aryana_maria2323 · Answer

Is -2192 the answer?

fibonaccichick666 · Answer

uh well, you are ahead of me at the moment.  I didn't have paper out, but if you plug and chugged, it should be right

fibonaccichick666 · Answer

yep, I got the same

aryana_maria2323 · Answer

Yayy! Thank you so much!

fibonaccichick666 · Answer

np, you did it