F(X) =x^2+4x-12... Root if F (x+1)=0?

Question

Please help me... I have the exercise done in a book but I don't understand where a number is coming from...

I wrote:

F(x+1)= (x+1)^2 + 4 (x +1) - 12

I get::::: x^2 + 1 + 4X + 4 - 12

But the book says::: x^2 + 2x + 1 + 4x + 4 - 12

where is the 2x coming from??? HELP ME PLEASE.
THANK YOU.

Answer 1

it's from the square

(x+1)^2 + 4(x+1) - 12

(x+1)(x+1) + 4(x+1) - 12

x^2 + x +x +1 + 4x + 4 - 12

x^2 + 2x + 1 + 4x + 4 - 12

x^2 + 6x - 7

Answer 2

(x + 1)(x + 1) = x^2 + 1x + 1x + 1 <-- here is where you miscalculated. (x+1)^2 = x^2 + 2x + 1 (FOIL)

x^2 + 4x -12 = x^2 + 2x + 1 + 4x + 4 - 12

Answer 3

f(x+1)=(x+1)^2+4(x+1)-12
x^2+2x+1+4x+4-12

The 2x comes from this:
x^2+x+x+1
x^2+2x+1

I hope this helps!