5x2=21x-4

Solution for 5x2=21x-4 equation:

5x^2=21x-4

We move all terms to the left:

5x^2-(21x-4)=0

We get rid of parentheses

5x^2-21x+4=0

a = 5; b = -21; c = +4;
Δ = b2-4ac
Δ = -212-4·5·4
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-19}{2*5}=\frac{2}{10}
=1/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+19}{2*5}=\frac{40}{10}
=4
$