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cos8A cos5A - cos12A cos9A / sin8A cos5A + cos12A sin9A = tan4A

cos8A cos5A - cos12A cos9A / sin8A cos5A + cos12A sin9A = tan4A

Grade:11

2 Answers

Vivek kumar
15 Points
5 years ago
Because tanA=sinA/cosA
By using identies of the chapter 9 some application of trigonometry you will be able to find out than the equation 
Cos8A cos5A - cos12A cos9A/sin8A cos5A + cos12A sin9A = tan4A
Arun
25750 Points
5 years ago
(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
 
 
Regards
Arun (askIITians forum expert)

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