5x^2+-x-21=0

Solution for 5x^2+-x-21=0 equation:

5x^2+-x-21=0

We add all the numbers together, and all the variables

5x^2-1x=0

a = 5; b = -1; c = 0;
Δ = b2-4ac
Δ = -12-4·5·0
Δ = 1
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1}=1$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-1}{2*5}=\frac{0}{10}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+1}{2*5}=\frac{2}{10}
=1/5
$