Question

show that 4cos12°cos48°cos 72°=36​

Answer 1

here is your answer.

Answer 2

ANSWER:--------------

{ 4cos12cos48cos72}

===>[2(2cos12cos48)cos72]

===>2[cos(12+48)+cos(12-48)]cos72

===>2(cos60+cos36)cos72

===>2cos60cos72+2cos36cos72

===>2×1/2×cos72+[cos(36+72)+cos(36-72)]

===>cos72+cos108+cos36

===>2cos(72+108)/2cos(72-108)/2+cos36

===>2cos90cos18+cos36

===>cos36(Proved)

note=[∵]

cos90°=0]

hope it helps:--

T!—!ANKS!!!!