4.6 z^2y-2,2xy+7y^3-(7,8xy-3,4x^2y+7y^2)
При 1)х=2,у=5; 2)х-2,у=3

4,6x²y-2,2xy+7y³-7,8xy+3,4x²y-7y²=8x²y-10xy+7y³-7y²1)x=2,y=58*4*5-10*2*5+7*125-7*25=160-100+875-175=7602)x=2,y=38*4*3-10*2*3+7*27-7*9=96-60+189-63=162