Can you prove that ? cos2θ = 2cos^2θ-1 ......thanks

1 Answer
Shreya
Mar 9, 2018

see below

Explanation:

We have,#cos2theta=cos(theta+theta)#
Or,applying #cos(a+b)=cosacosb-sinasinb#,we see,
#cos2theta=costheta xxcostheta-sinthetaxxsintheta#
=#cos^2theta-(1-cos^2theta)# {since #cos^2theta+sin^2theta=1#}
=#2cos^2theta-1# {#color(red)("Hence " proved)#}

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