若M=3x^2-8xy+9y^2-4x+6y+13,x,y为实数,试判断M的符号

若M=3x^2-8xy+9y^2-4x+6y+13,证明：M>0 若M=3x^2-8xy+9y^2-4x+6y+13,x,y为实数,试判断M的符号 已知2x²+xy=M,3y²+2xy=N,求4x²+8xy+9y² 通分:x-y/2x+2y与xy/(x+y)^2 ,2mn/4m^2-9与2m-3/2m+3格式：例如：x-y/2x+2y与xy/(x+y)^2最简公分母是.x-y/2x+2y=.xy/（x+y）^2=. 若x+y的平方等于x-y的平方+m,则m=（ ）A 2xy B -2xy C 4xy D-4xy 1 x²y-3xy²2 2x(2x-y)+y(y-2x)3 -6x(m-2n)+12(2n-m)4 3(y-x)²-(x-y)³5 4a²-366 (x-2y)²-x²7 4x³y+4x²y²+xy³8 (x+y)²-2m(x+y)+m²9 x²-9x+1810 -8x²-10x-3 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 已知2x+xy=10,3y+2xy=6.求4x+8xy+9y=? 若(2x-y-3)是4x^2-4xy+y^2-m的一个因式则m= 若（x+1)^2+|y-2|=0,求3x^2-[5xy-(x^2y-3xy)+4x^2y-8xy]的值 若x-y=4,xy=1,求(-2xy+2x+3y)-(3xy+2y-2x)-(x+4y+xy)的值 若x-y=4,xy=1,则(2x+y-2xy)-(3x+2y+xy)-(4xy+3y-5x)= 若(3x^2y-2xy^2)/M=-3x+2,则单项式M等于（ ） A.xy B.-xy C.x D.-y x-y=9,xy=8,则x²+y²=?x^m=a,x^n=b,则x^(3m-2n)=? 化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy] （-3x^y+2xy)-( )=4x^+xy 1.[(-3xy)^2*x^3-2x^2*(3xy^2)^3*1/2y]除以9x^4y^2=2.若a(x^3m)y^12/(3(x^2)y^2n)=4x^6y^8求2m+n-a 证明:无论x、y为何值时,M=3x^2-8xy+9y^2-4x+6y+13恒为非负数