12=5x^2+2x

Solution for 12=5x^2+2x equation:

12=5x^2+2x

We move all terms to the left:

12-(5x^2+2x)=0

We get rid of parentheses

-5x^2-2x+12=0

a = -5; b = -2; c = +12;
Δ = b2-4ac
Δ = -22-4·(-5)·12
Δ = 244
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{244}=\sqrt{4*61}=\sqrt{4}*\sqrt{61}=2\sqrt{61}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-2\sqrt{61}}{2*-5}=\frac{2-2\sqrt{61}}{-10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+2\sqrt{61}}{2*-5}=\frac{2+2\sqrt{61}}{-10}
$