0=1x+10x^2-21

Solution for 0=1x+10x^2-21 equation:

0=1x+10x^2-21

We move all terms to the left:

0-(1x+10x^2-21)=0

We add all the numbers together, and all the variables

-(1x+10x^2-21)=0

We get rid of parentheses

-10x^2-1x+21=0

a = -10; b = -1; c = +21;
Δ = b2-4ac
Δ = -12-4·(-10)·21
Δ = 841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{841}=29$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-29}{2*-10}=\frac{-28}{-20}
=1+2/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+29}{2*-10}=\frac{30}{-20}
=-1+1/2
$