X(x+15)=70

Solution for X(x+15)=70 equation:

X(X+15)=70

We move all terms to the left:

X(X+15)-(70)=0

We multiply parentheses

X^2+15X-70=0

a = 1; b = 15; c = -70;
Δ = b2-4ac
Δ = 152-4·1·(-70)
Δ = 505
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{-(15)-\sqrt{505}}{2*1}=\frac{-15-\sqrt{505}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+\sqrt{505}}{2*1}=\frac{-15+\sqrt{505}}{2}
$