SOLUTION: How do you prove sin2a=2tana/1+tan^2a?

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Question 1008447: How do you prove sin2a=2tana/1+tan^2a?
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
How do you prove sin2a=2tana/1+tan^2a?
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It's ambiguous.
Is sin2a sin(2a) or sin^2(a)?
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Assuming sin(2a):
2sin*cos = 2tan/(sec^2)
sin*cos = (sin/cos)*(1/cos^2)
sin*cos = (sin*cos^2/cos)= sin*cos
QED
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PS If anyone can show where working only 1 side makes a difference I would like to see it.