ive gotten it down from the original form to this

cos^2xcos^2y-sin2xsin^2y=cox^2x-sin^2y

but the next step i keep messing up even though im positive i knwo what im doing on it...someone help please...i knwo we have some smart people on here so help a brutha out

 

Are you trying to write:

cos^2 x or cos^2x

cos squared times x

or

cos to the power of 2x

 

nevermind...I was wrong

 

i meant cos square times x

 

is that supposed to be a sin^2x on the left hand of the equation or a sin(2x)?

 

sin^2x

sorry

 

what was the original form?

 

cos(x+y)cos(x-y)=cox^2x-sin^2y

 

 

cos(x+y)cos(x-y)=(cosxcosy-sinxsiny)(cosxcosy+sinxsiny)
=(cosxcosy)^2-(sinxsiny)^2 ;(use (a+b)(a-b)=a^2-b^2)
=cos^2xcos^2y-sin^2xsin^2y
=cos^2x(1-sin^2y)-sin^2x(1-cos^2y)
=cos^2x-cos^2xsin^2y-sin^2x+sin^2xcos^2y
=cos^2x-sin^2y