A=8x^2-26x+15

Solution for A=8x^2-26x+15 equation:

=8A^2-26A+15

We move all terms to the left:

-(8A^2-26A+15)=0

We get rid of parentheses

-8A^2+26A-15=0

a = -8; b = 26; c = -15;
Δ = b2-4ac
Δ = 262-4·(-8)·(-15)
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$A_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(26)-14}{2*-8}=\frac{-40}{-16}
=2+1/2
$
$A_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(26)+14}{2*-8}=\frac{-12}{-16}
=3/4
$