sin�0�5α = (1 - cos(2α))/2，cos�0�5α = (1 + cos(2α))/2cos�0�5(π/8) - sin�0�5(π/8)= [1 + cos(π/4)]/2 - [1 - cos(π/4)]/2= cos(π/4)= √2/2
原式=cosπ/4=√2/2
