-21x^2-20x+4=4

Solution for -21x^2-20x+4=4 equation:

-21x^2-20x+4=4

We move all terms to the left:

-21x^2-20x+4-(4)=0

We add all the numbers together, and all the variables

-21x^2-20x=0

a = -21; b = -20; c = 0;
Δ = b2-4ac
Δ = -202-4·(-21)·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20}{2*-21}=\frac{0}{-42}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20}{2*-21}=\frac{40}{-42}
=-20/21
$