f(4/3)+f(-4/3)
f(-4/3)=f(-4/3+1)+1
=f(-1/3)+1
= f(-1/3+1)+1
=f(2/3)+1
=-cos[π*(2/3)] +1
=1/2+1=3/2
f(4/3) =-cos[π*(4/3)]=1/2,
则f(4/3)+f(-4/3)=3/2+1/2=2.答案是3计算f(-1/3)时算错了f(-4/3)=f(-4/3+1)+1=f(-1/3)+1= 【f(-1/3+1)+1】+1=f(2/3)+2=-cos[π*(2/3)] +2=1/2+2=5/2f(4/3) =-cos[π*(4/3)]=1/2,则f(4/3)+f(-4/3)=5/2+1/2=3.我想问一下 这个 -cos[π*(4/3)]=？ 用口算怎么算利用诱导公式：cos（π+θ）=-cosθ,所以-cos[π*(4/3)]=-cos[π+π/3]= cos(π/3)=1/2