Question

If f(x)=x^2+4x, find the value(s) of x if the f(x) is 5.

Answer 1

The answer from the back of my text book is 1,-5.. how?

Answer 2

I thought I have to do:

\[f(x) = x ^{2}+4x\]
\[5=x ^{2}\]

Answer 3

+4x

Answer 4

and from there on, I am stuck.

Answer 5

it does for my other questions. But for this one I don't think that's how I should solve my question D:

Answer 6

It's the only way :X you just substitute X by the value given, wich in this case is 5

Answer 7

f(x) = x^2 + 4x
f(x) = 5

when you plug it in...
5 = x^2 + 4x

can you get the two values for x from here?

Answer 8

5= x^2 + 4x( subtract 5 )
x^2 + 4x - 5 = 0 ( quadratic)
( x +5) ( x- 1)= 0 ( factors)

x= -5 and x= 1

Answer 9

no I can't because I forgot how to do this D:

Answer 10

ohhhhh!!!

Answer 11

factored form! thank you!!