解方程：e的x次方+e的负x次方=3

题目

解方程：e的x次方+e的负x次方=3

答案

令y = e^x,原方程变为y + 1/y = 3
y^2 -3y + 1 = 0
y = (3±√5)/2
x = lny = ln(3±√5) - ln2