解
2(x+3y-2xy)-(4x+8y-2xy)
=2x+6y-4xy-4x-8y+8xy
=-2x-2y+4xy
=-2(x+y)+4xy
=-2×5+4×3
=12-10
=2
4x²-3y²=?不对 我有答案第一题=-16第二题=52但是没有过程2(x+3y-2xy)-(4x+8y-2xy)=2x+6y-4xy-4x-8y+2xy=-2x-2y-2xy=-2(x+y)-2xy=-2×5-2×3=-16不好意思，错了4x²-3y²=7 ①3x²+2y²=19②①+②得：7x²-y²=26∴14x²-2y²=2(7x²-y²)=2×26=52