solve quadratic formula
x-2x-15=0the first x is squared

You said that  x² - 2x - 15 = 0 .You could factor the left side:(x + 3) (x - 5) = 0This equation is true if either of the factors is zero.First factor:x + 3 = 0x = -3Second factor:x - 5 = 0x = 5

[tex] x^2-2x-15=0\\
x^2-5x+3x-15=0\\
x(x-5)+3(x-5)=0\\
(x+3)(x-5)=0\\
x=-3 \vee x=5
[/tex]