Question

cos2B+cos2A/cos2B-cos2A=cot(A+B) cot(A-B)

Answer 1

(cos 2B + cos 2A) / (cos 2B - cos 2A)

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

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

= cot (A + B) cot (A - B)

Hope this helps you :)