21x2=100

Solution for 21x2=100 equation:

21x^2=100

We move all terms to the left:

21x^2-(100)=0

a = 21; b = 0; c = -100;
Δ = b2-4ac
Δ = 02-4·21·(-100)
Δ = 8400
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:

$\sqrt{\Delta}=\sqrt{8400}=\sqrt{400*21}=\sqrt{400}*\sqrt{21}=20\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-20\sqrt{21}}{2*21}=\frac{0-20\sqrt{21}}{42}
=-\frac{20\sqrt{21}}{42}
=-\frac{10\sqrt{21}}{21}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+20\sqrt{21}}{2*21}=\frac{0+20\sqrt{21}}{42}
=\frac{20\sqrt{21}}{42}
=\frac{10\sqrt{21}}{21}
$