附加數學 - 複角

1
(1+tan A)/(1-tan A)=(1+sinA/cosA)/(1-sinA/cosA)
=(cosA+sinA)/(cosA-sinA)
=Both upper and lower times (cosA+sinA)
=(1+sin2A)/cos2A
=tan 2A + sec 2A


2
cot (A/2) - cot A=(cosA/2)/(sinA/2)-(cosA)/(sinA)
=(sinAcosA/2-cosAsinA/2)/sinAsin(a/2)
AS sinAcosA/2-cosAsinA/2=Sin(A-A/2)=sinA/2
=sin(A/2)/sinAsin(A/2)
=1/sinA=cscA