(X+5)(x-4)=70

Solution for (X+5)(x-4)=70 equation:

(X+5)(X-4)=70

We move all terms to the left:

(X+5)(X-4)-(70)=0

We multiply parentheses ..

(+X^2-4X+5X-20)-70=0

We get rid of parentheses

X^2-4X+5X-20-70=0

We add all the numbers together, and all the variables

X^2+X-90=0

a = 1; b = 1; c = -90;
Δ = b2-4ac
Δ = 12-4·1·(-90)
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-19}{2*1}=\frac{-20}{2}
=-10
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+19}{2*1}=\frac{18}{2}
=9
$