Good work

Your mistake is where I have bolded it - You have introduced a square root and then forgotten about it in the next step!99 = x^2 + 2x

99 - 2x = x^2

sqrt(99 - 2x) = x

(99 - 2x) / x = x97 = x

99 - 2 = x

x-intercept is (97, 0)

Sam

Instead you should try and factor it: what two numbers multiply to -99 and add to 2?

Hint: consider the factors of 99