Question

Prove that
(Cos8A.Cos5A - Cos12A.Cos9A )/(Sin8A.Cos5A+Cos12ASin9A)

Answer 1

Step-by-step explanation:

Solution

(cos8A.cos5A-cos12A.cos9A)/(sin8A.cos5A+cos12A.sin9A)

=> [1/2 {cos13A+cos3A}-1/2 {cos21A+cos3A}]/[1/2 {sin13A+sin3A}+1/2 {sin21A-sin3A}]

=>( cos13A-cos21A)/(sin13A+sin21A)

=> 2sin17A.sin4A/2sin17A.cos4A

=> tan4A