36-21x=-3x2

Solution for 36-21x=-3x2 equation:

36-21x=-3x^2

We move all terms to the left:

36-21x-(-3x^2)=0

We get rid of parentheses

3x^2-21x+36=0

a = 3; b = -21; c = +36;
Δ = b2-4ac
Δ = -212-4·3·36
Δ = 9
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{9}=3$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-3}{2*3}=\frac{18}{6}
=3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+3}{2*3}=\frac{24}{6}
=4
$