Math Is Fun Forum

tony123

Member

Registered: 2007-08-03

Posts: 229

cos(x - y)

Prove that if

and

,
then

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

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: cos(x - y)

Easy!

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: cos(x - y)

By inspection,

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

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: cos(x - y)

You need to do a bit more work than that.

greenisfab88

Member

Registered: 2008-11-24

Posts: 3

Re: cos(x - y)

I have troublr with that too.
i need help!

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: cos(x - y)

By the way, you also need the condition

to ensure that

and

are not both

.

jonecox

Member

Registered: 2010-01-20

Posts: 3

Re: cos(x - y)

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

sameer mishra

Member

Registered: 2010-08-27

Posts: 64

Re: cos(x - y)

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

sameer mishra

Member

Registered: 2010-08-27

Posts: 64

Re: cos(x - y)

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