x^2+3x-7=(x+3/2)^2-37/4=(x+3/2+genhao37/2)(x+3/2-genhao37/2)
x^2+2xy-5y^2=(x+y)^2-6y^2=(x+y+genhao6 y)(x+y-genhao6 y)
x^2+3xy-7y^2=(x+3/2 y)^2-37/4 y^2=(x+3/2y+genhao37 y/2)(x+3/2y-genhao37 y/2)