4x^2-7x+2=0
x^2-7x/4+1/2=0
x^2-7x/4+49/64-49/64+32/64=0
(x-7/8)^2-17/64=0
(x-7/8-√17/8)(x-7/8+√17/8)=0
x=7/8+√17/8或x=7/8-√17/8