Question

-х в квадрате -2х +15=0

Answer 1

$\displaystyle -x^2-2x+15=0\\\\x^2+2x-15=0\\\\\text{D}=4+\cdot4\cdot15=4+60=64=8^2\\\\x_1=\frac{-2+8}{2}=\frac{6}2=\boxed{3}\\\\x_2=\frac{-2-8}2=\frac{-10}2=\boxed{-5}$