x2=99-15x

Solution for x2=99-15x equation:

x2=99-15x

We move all terms to the left:

x2-(99-15x)=0

We add all the numbers together, and all the variables

x2-(-15x+99)=0

We add all the numbers together, and all the variables

x^2-(-15x+99)=0

We get rid of parentheses

x^2+15x-99=0

a = 1; b = 15; c = -99;
Δ = b2-4ac
Δ = 152-4·1·(-99)
Δ = 621
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{621}=\sqrt{9*69}=\sqrt{9}*\sqrt{69}=3\sqrt{69}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-3\sqrt{69}}{2*1}=\frac{-15-3\sqrt{69}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+3\sqrt{69}}{2*1}=\frac{-15+3\sqrt{69}}{2}
$