Question

4cosx cos2x cos3x=1,if 0 14 years ago

Answer 1

What's that, solve or prove true?

Answer 2

Cos nx = 2 cos x cos(n-1)x -cos(n-2)x

Answer 3

2(2cosxcos3x)cos2x=1
2(cos2x+cos4x)cos2x=1
2(cos2x)^2+2cos2xcos4x=1
2(cos2x)^2+cos6x+cos2x=1\[2\cos ^{2}2x-1+\cos6x+\cos2x=0\]
cos4x+cos6x+cos2x=0
cos4x+2cos4xcosx=0
cos4x(1+2cosx)=0
cos4x=0 or cosx=-1/2
x=90 or x=120

Answer 4

http://www.wolframalpha.com/input/?i=4+cosx+cos+2x+cos+3x+%3D1

Answer 5

4cosx cos 2x cos3x=1
(2cosx cos3x)(2cos2x)=1
(cos4x+cos2x)(2cos2x)=1
2cos4x cos2x+2cos^2 2x-1=0
2cos4x cos2x+cos4x=0
cos4x(2cos2x+1)=0
cos4x=0
2cos2x+1=0

Answer 6

Thats what exactly i have written.............thanks for verifying my answer

Answer 7

thanks to u man,i was just checking it out