Question

6. Prove that cos 48º.cos 12° = 3 + V5
8​

Answer 1

Answer:

cos 48°. cos 12° = 3+√5 by 8

LHS:

= 1/2[2 cos 48°.cos 12°]

= 1/2[cos (48+12)+cos (48-12)]

= cos 60° + cos 36°

= 1/2 [ 1/2+√5+1 by 4]

= 1/2 [ 2+√5+1 by 4]

= 1/2 × 3+√5 by 4]

= 3+√5 by 8

= RHS

Hence proved.