x-4√x+3=0 , x≥0
x+3=4√x
(x+3)²=(4√x)²
x²+6x+9=16x
x²-10x+9=0
(x-1)(x-9)=0 (Viet)
x1=1 , x2=9
(ab=0 ⇔ a=0 ∨ b=0)
x²-10x+9=0, D=100-36=64, √64=8
x1=(10-8)/2=2/2=1
x2=(10+8)/2=18/2=9
