X(x+7)=15

Solution for X(x+7)=15 equation:

X(X+7)=15

We move all terms to the left:

X(X+7)-(15)=0

We multiply parentheses

X^2+7X-15=0

a = 1; b = 7; c = -15;
Δ = b2-4ac
Δ = 72-4·1·(-15)
Δ = 109
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{-(7)-\sqrt{109}}{2*1}=\frac{-7-\sqrt{109}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(7)+\sqrt{109}}{2*1}=\frac{-7+\sqrt{109}}{2}
$