∵x,y,a,b分别是多项式4\1m^3n^2+3m^2n-4m-5的项数、最高项的系数、次数、常数项
∴x=4y=1/4a=5b=-5
∴7xy(a+b)-3(xy)^2+b\2a
=7*4*1/4*(5-5)-3*(4*1/4)²+(2*5)/(-5)
=0-3-2
=-5