y=[e^x+e^(-x)]/2 2y = e^x + e^(-x)2y e^x = (e^x)^2 + 1(e^x)^2 - 2y e^x + 1 = 0e^x = [2y ±√(4y^2 -4)]/2 = y ±√(y^2 -1)其中y -√(y^2 -1)= 1/[y +√(y^2 -1)]< 1/y同时y=[e^x+e^(-x)]/2≥2 √[e^x * e^(-x...