Need help with proofs, please!

  • Thread starter yvette25
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  • #1
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Homework Statement



prove:
sin3x = sinx (3-4sin^2x)

tanx+sinx/2tanx = cos^2(x/2)

cot2x = (cot^2 x-1)/(2cotx)

Homework Statement





Homework Equations





The Attempt at a Solution

 
Last edited:

Answers and Replies

  • #2
rock.freak667
Homework Helper
6,223
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....where is your attempt?
But anyhow...for the first one...rewrite sin3x as sin(2x+x)

and well for the second and third ones..try simplifying it into sin and cos only , for the last one...remember that cot(x)=1/tan(x)
 

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