Find the value for the function

Question

I'm getting the wrong answer to the following question.

Find f(x + 1) when f(x) = x² - 9 / x + 3

i added 1 to each portion of the formula to get

x² + x - 8 / 2x + 4

the correct answer is x² + 2x - 8 / x + 4

Answer 1

f(x) = (x^2 - 9)/(x+3) = (x-3)(x+3)/(x-3) = x-3

f(x) = x-3

f(x+1) = x+1-3 = x-2

f(x+1) = ((x+1)^2 -9)/((x+1)+3) = (x^2+2x+1 - 9)/(x+1+3) = (x^2+2x-8)/(x+4)= (x-2)(x+4)/(x+4) = x-2

replace x with x+1

(x^2+2x-8)/(x+4) is the correct answer. It can be simplified by canceling the factor x+4, to get x-2

Unless, you really meant

f(x) =x^2 -9/x -3

then f(x+1) = (x+1)^2 -9/(x+1) -3 = x^2 + 2x +1 - 9/(x+1) - 3 = x^2 +2x -2 - 9/(x+1)

but that seems unlikely that you meant that. You just left out some parentheses

what you did was add x+1 to both numerator and denominator, but f(x+1) means replace x with x+1, not to add x+1