105=-5x^2+50x

Solution for 105=-5x^2+50x equation:

105=-5x^2+50x

We move all terms to the left:

105-(-5x^2+50x)=0

We get rid of parentheses

5x^2-50x+105=0

a = 5; b = -50; c = +105;
Δ = b2-4ac
Δ = -502-4·5·105
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-50)-20}{2*5}=\frac{30}{10}
=3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-50)+20}{2*5}=\frac{70}{10}
=7
$