(x-3)(x+10)=55

Solution for (x-3)(x+10)=55 equation:

(x-3)(x+10)=55

We move all terms to the left:

(x-3)(x+10)-(55)=0

We multiply parentheses ..

(+x^2+10x-3x-30)-55=0

We get rid of parentheses

x^2+10x-3x-30-55=0

We add all the numbers together, and all the variables

x^2+7x-85=0

a = 1; b = 7; c = -85;
Δ = b2-4ac
Δ = 72-4·1·(-85)
Δ = 389
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{-(7)-\sqrt{389}}{2*1}=\frac{-7-\sqrt{389}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+\sqrt{389}}{2*1}=\frac{-7+\sqrt{389}}{2}
$