题目应是 化简:(1):4m-7n-2(m-2n).(2):-(x²-2xy-y²)+(5x²-2xy-3y²).
(1):4m-7n-2(m-2n)
=4m-7n-2m+4n
=2-3n
(2):-(x²-2xy-y²)+(5x²-2xy-3y²)
= -x²+2xy+y²+5x²-2xy-3y²
=4x²-2y²
题目应是 化简:(1):4m-7n-2(m-2n).(2):-(x²-2xy-y²)+(5x²-2xy-3y²).
(1):4m-7n-2(m-2n)
=4m-7n-2m+4n
=2-3n
(2):-(x²-2xy-y²)+(5x²-2xy-3y²)
= -x²+2xy+y²+5x²-2xy-3y²
=4x²-2y²