21x^2-57+30=0

Solution for 21x^2-57+30=0 equation:

21x^2-57+30=0

We add all the numbers together, and all the variables

21x^2-27=0

a = 21; b = 0; c = -27;
Δ = b2-4ac
Δ = 02-4·21·(-27)
Δ = 2268
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:

$\sqrt{\Delta}=\sqrt{2268}=\sqrt{324*7}=\sqrt{324}*\sqrt{7}=18\sqrt{7}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-18\sqrt{7}}{2*21}=\frac{0-18\sqrt{7}}{42}
=-\frac{18\sqrt{7}}{42}
=-\frac{3\sqrt{7}}{7}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+18\sqrt{7}}{2*21}=\frac{0+18\sqrt{7}}{42}
=\frac{18\sqrt{7}}{42}
=\frac{3\sqrt{7}}{7}
$