cos[兀/3 + arc sin(-1/2)] 的值
问题描述：
cos[兀/3 + arc sin(-1/2)] 的值
答
∵-π/2≦arc sinx≦π/2
∴arc sin(-1/2)=-π/6
cos[兀/3 + arc sin(-1/2)]=cos[兀/3 -π/6]=cos(π/6)=√3/2