156.25=x^2+72.25-8.5x

Solution for 156.25=x^2+72.25-8.5x equation:

156.25=x^2+72.25-8.5x

We move all terms to the left:

156.25-(x^2+72.25-8.5x)=0

We get rid of parentheses

-x^2+8.5x-72.25+156.25=0

We add all the numbers together, and all the variables

-1x^2+8.5x+84=0

a = -1; b = 8.5; c = +84;
Δ = b2-4ac
Δ = 8.52-4·(-1)·84
Δ = 408.25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8.5)-\sqrt{408.25}}{2*-1}=\frac{-8.5-\sqrt{408.25}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8.5)+\sqrt{408.25}}{2*-1}=\frac{-8.5+\sqrt{408.25}}{-2}
$