# question help: I have a calculus question that i dont understand. - Help.com

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## I have a calculus question that i dont understand.

f(4x-1)=-(4x-1)(squared)+6(4x-1)-11
that should = -16x(squared)+24x-18
but in my textbook it shows up as -16x(squared)+32x-18
The same goes for my other questions, there the same except the numbers are changed and I keep getting the one number wrong every question. Where does that extra 8x come from?

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I have a calculus answer that is most likely incorrect :-(

-(4x - 1)^2=-(16x^2 - 8x + 1)

etc. you didn’t FOIL properly, did you? ;p

no no the f(4x-1) is just a function notation or whatever. Just say its f=-(4x-1)^2….etc

Llama790 wrote:
no no the f(4x-1) is just a function notation or whatever. Just say its f=-(4x-1)^2….etc

huh? clearly, in this case
f(x) = x^2 + 6x - 11
and then (4x-1) is substituted in for x. where’s the problem?

the question is f=-(4x-1)^2+6(4x-1)-11
=-16x^2-1+24x-6-11
=-16x^2+24x-18
but in my textbook the answer is
-16x^2+32x-18
where does that 32x come from

ok, I’ll walk you through it.

=-(4x - 1)^2 + 6(4x - 1) - 11

=-(16x^2 - 8x + 1) + (24x - 6) - 11

=-16x^2 + 32x - 18

This isn’t as much calculus as it is algebra and expanding the brackets.

so basically,

= -[(4x-1)(4x-1)] + 6(4x - 1) - 11
= -(16x^2 - 4x - 4x +1) + 24x - 6 - 11
= - 16x^2 + 8x - 1 + 24x - 6 - 11
= - 16x^2 + 32x - 18

The textbook is right.

I think your problem is thinking that

(4x - 1)^2 = (4x)^2 + (-1)^2

ty :)

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