(7a-15)(9a+25)=90

Solution for (7a-15)(9a+25)=90 equation:

(7a-15)(9a+25)=90

We move all terms to the left:

(7a-15)(9a+25)-(90)=0

We multiply parentheses ..

(+63a^2+175a-135a-375)-90=0

We get rid of parentheses

63a^2+175a-135a-375-90=0

We add all the numbers together, and all the variables

63a^2+40a-465=0

a = 63; b = 40; c = -465;
Δ = b2-4ac
Δ = 402-4·63·(-465)
Δ = 118780
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{118780}=\sqrt{4*29695}=\sqrt{4}*\sqrt{29695}=2\sqrt{29695}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(40)-2\sqrt{29695}}{2*63}=\frac{-40-2\sqrt{29695}}{126}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(40)+2\sqrt{29695}}{2*63}=\frac{-40+2\sqrt{29695}}{126}
$