用五點法
就是y=0,y=1,y=-1
y=0,則2x+π/4=-π,x=-5π/8
2x+π/4=0,x=-π/8
2x+π/4=π,x=3π/8
y=1,2x+π/4=π/2,x=π/8
y=-1,2x+π/4=-π/2,x=-3π/8
所以五點是
(-5π/8,0),(-3π/8,-1),(-π/8,0),(π/8,1),(3π/8,0)
然后描出來就可以了