5x^2-12x=21

Solution for 5x^2-12x=21 equation:

5x^2-12x=21

We move all terms to the left:

5x^2-12x-(21)=0

a = 5; b = -12; c = -21;
Δ = b2-4ac
Δ = -122-4·5·(-21)
Δ = 564
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:

$\sqrt{\Delta}=\sqrt{564}=\sqrt{4*141}=\sqrt{4}*\sqrt{141}=2\sqrt{141}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-12)-2\sqrt{141}}{2*5}=\frac{12-2\sqrt{141}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-12)+2\sqrt{141}}{2*5}=\frac{12+2\sqrt{141}}{10}
$