Find all of the solutions of th equation cosx+cos2x=0

题目

Find all of the solutions of th equation cosx+cos2x=0

答案

求cosx+cos2x=0的所有解
解cosx+cos2x=0
cosx+2cosx^2-1=0
(2cosx-1)*(cosx+1）=0
cosx=1/2,cosx=-1
x1=2kπ+π/3,x2=2kπ-π/3
x3=2kπ+π ,k∈整数