(x+1)(x+2)=15

Solution for (x+1)(x+2)=15 equation:

(x+1)(x+2)=15

We move all terms to the left:

(x+1)(x+2)-(15)=0

We multiply parentheses ..

(+x^2+2x+x+2)-15=0

We get rid of parentheses

x^2+2x+x+2-15=0

We add all the numbers together, and all the variables

x^2+3x-13=0

a = 1; b = 3; c = -13;
Δ = b2-4ac
Δ = 32-4·1·(-13)
Δ = 61
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{-(3)-\sqrt{61}}{2*1}=\frac{-3-\sqrt{61}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+\sqrt{61}}{2*1}=\frac{-3+\sqrt{61}}{2}
$