cos(π/5＋x)=－1/2,则π/5＋x=2kπ＋2π/3或π/5＋x=2kπ－2π/3,解得x=2kπ＋7π/15或x=2kπ－13π/15.其中k是整数.还是看不懂厄 - -。就π/5＋x=2kπ＋2π/3或π/5＋x=2kπ－2π/3怎么算的。 配方还是啥？ 详细点么？余弦值等于－1/2的角是2kπ＋2π/3或2kπ－2π/3，则π/5＋x=2kπ＋2π/3或π/5＋x=2kπ－2π/3，解一下就可以了。