Y=x2-81

Solution for Y=x2-81 equation:

=Y2-81

We move all terms to the left:

-(Y2-81)=0

We add all the numbers together, and all the variables

-(+Y^2-81)=0

We get rid of parentheses

-Y^2+81=0

We add all the numbers together, and all the variables

-1Y^2+81=0

a = -1; b = 0; c = +81;
Δ = b2-4ac
Δ = 02-4·(-1)·81
Δ = 324
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{324}=18$
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-18}{2*-1}=\frac{-18}{-2}
=+9
$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+18}{2*-1}=\frac{18}{-2}
=-9
$