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**cos(x - y)**

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**tony123****Member**- Registered: 2007-08-03
- Posts: 192

Prove that if

and

,

then

*Last edited by tony123 (2008-11-22 22:30:46)*

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

Easy!

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**Daniel123****Member**- Registered: 2007-05-23
- Posts: 663

By inspection,

*Last edited by Daniel123 (2008-11-23 11:27:22)*

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

You need to do a bit more work than that.

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**greenisfab88****Member**- Registered: 2008-11-24
- Posts: 3

I have troublr with that too.

i need help!

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**JaneFairfax****Member**- Registered: 2007-02-23
- Posts: 6,868

By the way, you also need the condition

to ensure that and are not both .Offline

**jonecox****Member**- Registered: 2010-01-20
- Posts: 3

I know very well this expression.I am studying this function in school.I like your work.Thanks for share this information.

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**sameer mishra****Member**- Registered: 2010-08-27
- Posts: 64

cosx +cosy=a

sinx-siny=b

squarring bot the equation then subtrac

cos2x+cos2y+2cox(x-y)=a2-b2

2cos(x-y)[1+cos(x+y)]=a^2-b^2 (o)

now squarring above equation then add

cos(x+y)=(a^2+b^2)/2-1

now put the valu of cos(x+y) in (o)

cos(x-y)=a2 -b2/a2+b2

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**sameer mishra****Member**- Registered: 2010-08-27
- Posts: 64

hello JaneFairfax i think that you are intresested in trigo.

but i challange you in trigo. calculus algebra. coordinate pleaseeeeeeeee

accept my challenge and ask question from me

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**cos(x - y)**