化简求值: [(xy+2)(xy-2)-2x²y²+4]÷(xy), 其中x=20,y=- 1/25
问题描述:
化简求值: [(xy+2)(xy-2)-2x²y²+4]÷(xy), 其中x=20,y=- 1/25
答
[(xy+2)(xy-2)-2x²y²+4]÷(xy),
=﹙x²y²-4-2x²y²+4)÷(xy)
=(-x²y²)÷(xy)
=-xy
=-20×(-1/25)
=4/5