argz表示z的幅角,有A=arg(2+i),B=arg(-1+2i),则sin(A+B)=?

tgA=1/2,tgB=-2
sinA=1/5^(1/2),cosA=2/5^(1/2)
sinB=2/5^(1/2),cosB=-1/5^(1/2)
sin(A+B)=sinAcosB+sinBcosA
=(1/5^(1/2))*(-1/5^(1/2))+(2/5^(1/2))*(2/5^(1/2))
=-1/5+4/5=3/5