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## Topic review (newest first)

George,Y
2006-04-03 16:09:58

never mind, a systematic book is really helpful, hehe.

lkomarci
2006-04-02 06:02:13

i understand now, i borrowed some books from a local library and now i understand.
thank you George

George,Y
2006-04-01 13:31:55

Pythagoras' Theorem

tom a
2006-03-31 21:52:07

#### lkomarci wrote:

i've been doing integrals of trig functions because it's my weakest point.
there are a few basic things that i don't understand.

for eg. i KNOW that:

sin^2x=(1-Cos2x)/2
cos^2x=(1+Cos2x)/2

but please explain this, why is...

1-(Cos^2)2x = 1-Cos4x

and

(Cos^3)2x = (1-(Sin^2)2x)Cos2x

maths drags

lkomarci
2006-03-31 21:46:15

whoops sorry it's supposed to say..
1-(Cos^2)2x = 1+Cos4x

lkomarci
2006-03-31 21:45:00

i've been doing integrals of trig functions because it's my weakest point.
there are a few basic things that i don't understand.

for eg. i KNOW that:

sin^2x=(1-Cos2x)/2
cos^2x=(1+Cos2x)/2

but please explain this, why is...

1-(Cos^2)2x = 1-Cos4x

and

(Cos^3)2x = (1-(Sin^2)2x)Cos2x