sinα^2=[1-cos(2α)]/2
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ããsinα^2=[1-cos(2α)]/2
ããcosα^2=[1+cos(2α)]/2
ããtanα^2=[1-cos(2α)]/[1+cos(2α)]
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ããsin(2α)=2sinα·cosα=2/(tanα+cotα)
ããcos(2α)=cos²Î±-sin²Î±=2cos²Î±-1=1-2sin²Î±
ããtan(2α)=2tanα/[1-(tanα)²]
ããcot(2α)=(cot²Î±-1)/(2cotα)
ããsec(2α)=sec²Î±/(1-tan²Î±)
ããcsc(2α)=1/2secα·cscα