28+9=21x2

Solution for 28+9=21x2 equation:

28+9=21x^2

We move all terms to the left:

28+9-(21x^2)=0

We add all the numbers together, and all the variables

-21x^2+37=0

a = -21; b = 0; c = +37;
Δ = b2-4ac
Δ = 02-4·(-21)·37
Δ = 3108
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:

$\sqrt{\Delta}=\sqrt{3108}=\sqrt{4*777}=\sqrt{4}*\sqrt{777}=2\sqrt{777}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{777}}{2*-21}=\frac{0-2\sqrt{777}}{-42}
=-\frac{2\sqrt{777}}{-42}
=-\frac{\sqrt{777}}{-21}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{777}}{2*-21}=\frac{0+2\sqrt{777}}{-42}
=\frac{2\sqrt{777}}{-42}
=\frac{\sqrt{777}}{-21}
$