(x+40)(x-30)=0

Solution for (x+40)(x-30)=0 equation:

(x+40)(x-30)=0

We multiply parentheses ..

(+x^2-30x+40x-1200)=0

We get rid of parentheses

x^2-30x+40x-1200=0

We add all the numbers together, and all the variables

x^2+10x-1200=0

a = 1; b = 10; c = -1200;
Δ = b2-4ac
Δ = 102-4·1·(-1200)
Δ = 4900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4900}=70$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(10)-70}{2*1}=\frac{-80}{2}
=-40
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+70}{2*1}=\frac{60}{2}
=30
$