Question

show that 3cos^2-sin^2=1+2cos2x

Answer 1

use, cos2x = cos^2x-sin^2x

Answer 2

Solving right hand side first @hartnn

Answer 3

yup, easier

Answer 4

I will go with Left then..

Answer 5

let asker try first

Answer 6

i did use that rule but i got stuck there

Answer 7

which step exactly? can u show your work?

Answer 8

so that we can guide u from there

Answer 9

put cos^2(x)= 1/2 (1+cos2x) and sin^2(x)= 1/2 (1 - cos2x) to get the reqd ans

Answer 10

Show your work first @david warner..

Answer 11

i basically did it from the LHS .. used the cos(2x) rule .. so i hhad 3(cos2x) and then (3(2cos^2x-1)

Answer 12

thats where u did the mistake....its 3cos^2-sin^2 and not 3cos^2-3sin^2....
write cos^2(x)= 1/2 (1+cos2x) and sin^2(x)= 1/2 (1 - cos2x)

Answer 13

ohh i see it now .. thanku :)

Answer 14

welcome ^_^
ask if there are still doubts anywhere