4r2-90=2r

Solution for 4r2-90=2r equation:

4r^2-90=2r

We move all terms to the left:

4r^2-90-(2r)=0

a = 4; b = -2; c = -90;
Δ = b2-4ac
Δ = -22-4·4·(-90)
Δ = 1444
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1444}=38$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-38}{2*4}=\frac{-36}{8}
=-4+1/2
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+38}{2*4}=\frac{40}{8}
=5
$