1
1+sina=(sin(a/2))^2+(cos(a/2))^2+2sin(a/2)cos(a/2)
=(sin(a/2)+cos(a/2))^2
所以
原式=|sin(a/2)+cos(a/2)|+|sin(a/2)-cos(a/2)|
=-sin(a/2)-cos(a/2)-sin(a/2)+cos(a/2)
=-2sin(a/2)
(因为5Pi/4