What is square root of 4x + 13 = 2x -1

Hello : 
√(4x+13) = 2x-1(1)
note : if ( a=b) so (a² = b²)
if : (√(4x+13) )²= (2x-1)²  so : 4x+13 = 4x²-4x+1
4x²-8x-12 = 0
x²-2x-3 = 0
(x+1)(x-3) = 0
x+1 = 0  or x-3=0
x= -1 or x=3
if : x= -1 : √(4(-1)+13) = 2(-1)-1
√9 =-3   but √9 =3
3 = -3 impossible  ( -1 is not solution of equation (1)
if : x = 3 :   √(4(3)+13) = 2(3)-1
5 = 5  ( right) conclusion : one solution : 3