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## #1 2006-03-30 22:45:00

lkomarci
Member
Registered: 2005-08-24
Posts: 23

### integrating trigonometric functions

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

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## #2 2006-03-30 22:46:15

lkomarci
Member
Registered: 2005-08-24
Posts: 23

### Re: integrating trigonometric functions

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

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## #3 2006-03-30 22:52:07

tom a
Guest

### Re: integrating trigonometric functions

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

## #4 2006-03-31 14:31:55

George,Y
Member
Registered: 2006-03-12
Posts: 1,306

### Re: integrating trigonometric functions

Pythagoras' Theorem

X'(y-Xβ)=0

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## #5 2006-04-01 08:02:13

lkomarci
Member
Registered: 2005-08-24
Posts: 23

### Re: integrating trigonometric functions

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

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## #6 2006-04-02 18:09:58

George,Y
Member
Registered: 2006-03-12
Posts: 1,306

### Re: integrating trigonometric functions

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

X'(y-Xβ)=0

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