12.写出一个同时满足下列性质①②③的函数解析式:f(x)=f(x)=f(x)=___4x−14x+1\frac{{4}^{x}-1}{{4}^{x}+1}4x+14x−1[(答案不唯一) ].①定义域为RRR;②值域为(−1,1)(-1,1)(−1,1);③f(x)f(x)f(x)是奇函数.