(cos^2x) - (sin^2x) = 1-(2sin^2x)

2007-04-01 1:38 am

prove the following identities
(cos^2x) - (sin^2x) = 1-(2sin^2x)

有好多題數唔識，條條都係計到呢到唔識計落去－ｖ－
幫幫我＞＜

回答 (2)

2007-04-01 1:54 am

SINCE RHS=1-(2sin^2x)=1-sin^2x-sin^2x=(1-sin^2x)-sin^2x=cos^2x-sin^2x=LHS(cos^2x+sin^2x=1)

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2007-04-01 1:48 am

L.H.S. = (cos^2x) - (sin^2x)
= (1-sin^2x) - (sin^2x)
=1- sin^2x - sin^2x
= 1- 2sin^2x
= R.H.S.
Because L.H.S. = R.H.S.
Therefore it is an identity.

參考: me

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