sin(x+4分之3派)=sin(π-x-3π/4)=-sin(x-π/4)
f(x)=1/2cosx-1/2sinx=√2/2(sinπ/4cosx-cosπ/4sinx)=√2/2sin(π/4-x)=√2/2sin(π-π/4+x)
=√2/2sin(x+3π/4)=-√2/2sin(x-π/4)
答案是 -√2/2sin(x-π/4) 和 √2/2sin(x+3π/4) 是一样的.
sin(x+4分之3派)=sin(π-x-3π/4)=-sin(x-π/4)
f(x)=1/2cosx-1/2sinx=√2/2(sinπ/4cosx-cosπ/4sinx)=√2/2sin(π/4-x)=√2/2sin(π-π/4+x)
=√2/2sin(x+3π/4)=-√2/2sin(x-π/4)
答案是 -√2/2sin(x-π/4) 和 √2/2sin(x+3π/4) 是一样的.