Request a call back

Join NOW to get access to exclusive study material for best results

CBSE Class 11-science Answered

sir i had a ques: show that- cos6.cos42.cos66.cos78= 1/16
Asked by | 30 May, 2012, 04:33: PM
answered-by-expert Expert Answer

cos6.cos42.cos66.cos78
= (1/4) * [2cos6 cos66] * [2cos42 cos78]
= (1/4) * (cos72 + cos60) * (cos120 + cos36)
= (1/4) (cos72 + 1/2) * (- 1/2 + cos36)
= (1/4) [- 1/4 + (1/2) (cos36 - cos72) + cos36cos72]
= (1/4) [- 1/4 + sin54sin18 + sin54 sin18]
= (1/4) [- 1/4 + 2sin54 sin18 cos18 / cos18]
= (1/4) [- 1/4 + sin54 sin36 / cos18]
= (1/4) [- 1/4 + (cos18 - cos90) / 2cos18]
= (1/4) [- 1/4 + 1/2]
= 1/16

Answered by | 31 May, 2012, 10:18: AM
CBSE 11-science - Maths
Asked by rajyothi64 | 05 Mar, 2024, 09:49: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by ghoshshawata62 | 04 Mar, 2024, 08:16: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by nayaktapaswini2007 | 29 Feb, 2024, 09:10: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by bimanmandal53361 | 15 Jan, 2024, 12:32: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by sreyas.katuri | 23 Sep, 2023, 07:12: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by 069.pks | 16 Sep, 2023, 10:06: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by surekhashriwas01 | 12 Sep, 2023, 08:39: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by mvr23467 | 12 Sep, 2023, 07:52: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by SasipriyaNagappan | 27 Jul, 2023, 07:22: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 11-science - Maths
Asked by SasipriyaNagappan | 26 Jul, 2023, 06:55: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
Get Latest Study Material for Academic year 24-25 Click here
×