A=-x^2+13x+14

Solution for A=-x^2+13x+14 equation:

=-A^2+13A+14

We move all terms to the left:

-(-A^2+13A+14)=0

We get rid of parentheses

A^2-13A-14=0

a = 1; b = -13; c = -14;
Δ = b2-4ac
Δ = -132-4·1·(-14)
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-13)-15}{2*1}=\frac{-2}{2}
=-1
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-13)+15}{2*1}=\frac{28}{2}
=14
$