f(x, y) = f(x, z)⼀ f(y, z), 函数 f(x, y)？
f(x, y) = f(x, z)/ f(y, z), 函数 f(x, y)(a) f(x, y) = x / y (b) f(x, y) = 3x / y (c) f(x, y) = x2/y2(d) f(x, y) = (2x+1) / (2y+1) (e) f(x, y) = (2x2+1) / (2y2+1)(f) f(x, y) = (loge x) / (loge y) (g) f(x, y) = (loge (2x+1)) / (loge (2y+1)）
