原式=[2x^4+y^2+4x^2y-15y^2x^2-5y^2-4x^4+4y^2]/5x^2y
=[-2x^4+4x^2y-15y^2x^2]/5x^2y
=-0.4x^2/y+0.8-3y
代值
原式=-0.4*99^2*15/2+0.8-3*2/15
=-3*99^2+0.4
=-3(10000-200+1)+0.4
=-30000+600-3+0.4
解:(1)原式=[4x4+y2+4x2y-15y2x2-5y2-4x4+4y2]÷5x2y
=(4x2y-15y2x2)÷5x2y
=
45-3y,
当y=215时,原式=45-3×215=25;