x2-30x+225=400

Solution for x2-30x+225=400 equation:

x2-30x+225=400

We move all terms to the left:

x2-30x+225-(400)=0

We add all the numbers together, and all the variables

x^2-30x-175=0

a = 1; b = -30; c = -175;
Δ = b2-4ac
Δ = -302-4·1·(-175)
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-40}{2*1}=\frac{-10}{2}
=-5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+40}{2*1}=\frac{70}{2}
=35
$