(X+7)(x+2)=90

Solution for (X+7)(x+2)=90 equation:

(X+7)(X+2)=90

We move all terms to the left:

(X+7)(X+2)-(90)=0

We multiply parentheses ..

(+X^2+2X+7X+14)-90=0

We get rid of parentheses

X^2+2X+7X+14-90=0

We add all the numbers together, and all the variables

X^2+9X-76=0

a = 1; b = 9; c = -76;
Δ = b2-4ac
Δ = 92-4·1·(-76)
Δ = 385
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{-(9)-\sqrt{385}}{2*1}=\frac{-9-\sqrt{385}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+\sqrt{385}}{2*1}=\frac{-9+\sqrt{385}}{2}
$