25的X次幂=2000.80的Y次幂=2000.求X+Y-XY的值,要能看懂,不要用同底数幂的除法还没学到,急
问题描述:
25的X次幂=2000.80的Y次幂=2000.求X+Y-XY的值,要能看懂,不要用同底数幂的除法还没学到,急
答
25^x=2000
(25^X)^Y=2000^y
即25^xy=2000^y①
80^y=2000
(80^y)^x=2000^x
即80^xy=2000^x②
①*②得(25*80)^xy=2000^(x+y)
2000^xy=2000^(x+y)
故xy=x+y
X+Y-XY
=xy-xy
=0