已知f(α)=sin(π-α)cos(2π-α)/cos(-π-α)tanα,则f(-31/3π)的值为
问题描述:
已知f(α)=sin(π-α)cos(2π-α)/cos(-π-α)tanα,则f(-31/3π)的值为
答
∵f(α)=sinαcosα/-cosαtanα=-cosα
f(-31/3π)=)=-cos(10π+ π/3)==-cos(π /3)=-1/2