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

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

whoops sorry it's supposed to say..

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

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**tom a****Guest**

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)/2but please explain this, why is...

1-(Cos^2)2x = 1-Cos4xand

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

maths drags

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

Pythagoras' Theorem

**X'(y-Xβ)=0**

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

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

thank you George

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

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

**X'(y-Xβ)=0**

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