2x^2-8xy+5y^2
=(2x^2-8xy+8y^2)-3y^2
=(√2x-2√2y)^2-(√3y)^2
=(√2x-2√2y+√3y)(√2x-2√2y-√3y)
=[√2x-(2√2-√3)y][√2x-(2√2+√3)y]