0=15x^2-36x+21

Solution for 0=15x^2-36x+21 equation:

0=15x^2-36x+21

We move all terms to the left:

0-(15x^2-36x+21)=0

We add all the numbers together, and all the variables

-(15x^2-36x+21)=0

We get rid of parentheses

-15x^2+36x-21=0

a = -15; b = 36; c = -21;
Δ = b2-4ac
Δ = 362-4·(-15)·(-21)
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{36}=6$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(36)-6}{2*-15}=\frac{-42}{-30}
=1+2/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(36)+6}{2*-15}=\frac{-30}{-30}
=1
$