Y=x2-8x-9

Solution for Y=x2-8x-9 equation:

=Y2-8Y-9

We move all terms to the left:

-(Y2-8Y-9)=0

We add all the numbers together, and all the variables

-(+Y^2-8Y-9)=0

We get rid of parentheses

-Y^2+8Y+9=0

We add all the numbers together, and all the variables

-1Y^2+8Y+9=0

a = -1; b = 8; c = +9;
Δ = b2-4ac
Δ = 82-4·(-1)·9
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-10}{2*-1}=\frac{-18}{-2}
=+9
$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+10}{2*-1}=\frac{2}{-2}
=-1
$