這題我來試試看哈：
f(x)=sin(x+π/4)+2sin(x?π/4)?4cos2x+3cos(x+3π/4)
（1）當x=π/4時：
x+π/4=π/2 → sin=1
x?π/4=0 → sin=0
2x=π/2 → cos=0
x+3π/4=π → cos=?1
代入得：1 + 0 ? 0 + 3×(?1) = ?2
（2）當x=3π/4時：
x+π/4=π → sin=0
x?π/4=π/2 → sin=1
2x=3π/2 → cos=0
x+3π/4=3π/2 → cos=0
代入得：0 + 2×1 ? 0 + 0 = 2
搞定收工~
f(x)=sin(x+π/4)+2sin(x?π/4)?4cos2x+3cos(x+3π/4)
（1）當x=π/4時：
x+π/4=π/2 → sin=1
x?π/4=0 → sin=0
2x=π/2 → cos=0
x+3π/4=π → cos=?1
代入得：1 + 0 ? 0 + 3×(?1) = ?2
（2）當x=3π/4時：
x+π/4=π → sin=0
x?π/4=π/2 → sin=1
2x=3π/2 → cos=0
x+3π/4=3π/2 → cos=0
代入得：0 + 2×1 ? 0 + 0 = 2
搞定收工~