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问题: 函数

已知f(x)=e(x次方)-e(-x次方),
g(x)=e(x次方)+e(-x次方) e=2.71828.
设f(x)f(y)=4, g(x)g(y)=8

求g(x+y)/g(x-y)的值

解答:

由f(x)f(y)=4, g(x)g(y)=8 得:
e^(x+y)-e^(x-y)-e^[-(x-y)]+e^[-(x+y)]=4,
e^(x+y)+e^(x-y)+e^[-(x-y)]+e^[-(x-y)]=8,
即g(x+y)-g(x-y)=4,g(x+y)+g(x-y)=8,
∴g(x+y)=6,g(x-y)=2.
∴g(x+y)/g(x-y)=3.