I'm assuming ALL of 5x^2 - 3x is under the square root sign.
(√5x^2-3x)^2=(2x)^2 Square both sides5x^2-3x=4x^2 Simplify
5x^2 - 3x - 4x^2 = 4x^2 - 4x^2 Subtract 4x^2 from both sides
x^2 - 3x = 0 Simplify
Use the quadratic formula.
x = {-(-3) ± √(-3)^2 - 4(1)(0)}/2(1)= (3 ± √9 - 4)/2
= (3 ± √5)/2
x = 1.5 + (√5)/2 and 1.5 - (√5)/2