(14a+9)(5a-15)=0

Solution for (14a+9)(5a-15)=0 equation:

(14a+9)(5a-15)=0

We multiply parentheses ..

(+70a^2-210a+45a-135)=0

We get rid of parentheses

70a^2-210a+45a-135=0

We add all the numbers together, and all the variables

70a^2-165a-135=0

a = 70; b = -165; c = -135;
Δ = b2-4ac
Δ = -1652-4·70·(-135)
Δ = 65025
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{65025}=255$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-165)-255}{2*70}=\frac{-90}{140}
=-9/14
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-165)+255}{2*70}=\frac{420}{140}
=3
$