-7+1/2x^3y-x^2y^2/3-x^4+y^3是几次几项式? 最高次项是?

化简3(x-y)-7(x--y)+2(y-x) 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) 计算:1/(x-y)-1/(x+y)-2y/(x^2+y^2)-4y^3/(x^4+y^4)-8x^7/(x^8+y^8) x²/xy-x/y 3x/4x+y - x-2y/4x+y (1-y/y+x)÷x/y²-x² x(x-y)2-(y-x)3 [2/3x-2/x+y(x+y/3x-x-y)]/x-y/x 化简：{2/3x-2/(x+y)[(x+y)/3x-x-y]}/(x+y)/x 计算2/3x-2/x+y(x+y/3x-x-y)/x-y/x 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 化简3x-2/(x+y)[(x+y)/3x-x-y]÷(x-y)/x x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x 计算：x+2y/x-y+2x/y-x-3y/x-y 化简:(x-3y)(x+y)-(x-2y)(x+2y)-(x-y)平方 [(3x+y)(x-y)-(2x+3y)(x-y)]*(x-y) (-3x+7y)(-7y-3x)-(x-3y)(2x+3y) 18(x+y)^8(x-y)^7÷[3(x+y)^3(x-y)^3]^2 (3x-y)^2+(3x+y)(3x-y),x=1,y=-2