sin(1/5)=cos(π/2-1/5)
cos5=cos(-5)=cos(2π-5)
∵0＜π/2-1/5＜π/2
0＜2π-5＜π/2
(π/2-1/5)-(2π-5)
=24/5-3π/2=3/2(16/5-π)
=1.5(3.2-π)＞0
∴cos(π/2-1/5)＜cos(2π-5)
∴sin1/5＜cos5