請幫幫忙 plz

點樣prove tan(A+B)+tan(A-B)=2sin2A/cos2A+cos2B ??

tan(A+B)+tan(A-B)

= sin (A+B) / cos (A+B) + sin (A-B) / cos (A-B)

= [sin (A+B) cos (A-B) + sin (A-B) cos (A+B) ] / cos (A+B) cos (A-B)

= {1/2 [ sin 2A + sin 2B ] + 1/2 [ sin 2A - sin 2B ] }/(1/2)[cos2A+cos 2B]

=(sin2A+sin2B+sin2A-sin2B) / (cos2A+cos2B)

= 2sin 2A / (cos 2A + cos 2B)

點樣將tan(A+B)+tan(A-B)變成product?

tan(A+B)+tan(A-B)係無product既~~~

要變product 只可以轉成sin 或者cos