若m=x3-3x2y+2xy2+3y2 n=x3-2x2y+xy2-5y3,则2x3-7x2y+5xy2+14y2等于( )
问题描述：
若m=x3-3x2y+2xy2+3y2 n=x3-2x2y+xy2-5y3,则2x3-7x2y+5xy2+14y2等于( )
若m=x3-3x2y+2xy2+3y2 n=x3-2x2y+xy2-5y3,则2x3-7x2y+5xy2+14y2等于( )
空里用字母表示
答
3m-n
=3(x³-3x²y+2xy²+3y²)-(x³-2x²y+xy²-5y²)
=3x³-9x²y+6xy²+9y²-x³+2x²y-xy²+5y²
=2x³-7x²y+5xy²+14y²
所以
2x³-7x²y+5xy²+14y²=3m-n