I typed it in a hurry and made a little mistake, The first 3 lines are correct and then in the fourth line substitute 1-cos^2x for sin^2x.
Here is the correct solution.

first use cos(x+y)=cosxcosy-sinxsiny.

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)-(1-cos^2x)sin^2y
=cos^2x-cos^2xsin^2y-sin^2y+cos^2xsin^2y
=cos^2x-sin^2y.

 

good deal..thank you

 

Any time.. my friend

 

Forgive me, but I've never seen such craziness, I mean really. Who uses this stuff, and for what? Has this ever helped anyone (in the present) do anything?

 

i'm pretty sure you would need some of that stuff to shoot a rocket off and land a rover on Mars.

 

So this is now the homework forum???

 

hell yeah it is.....its the off topic and their aint no homework section so there we go lol

i dono if anyone would ever need to use this but all i know is that its in the course that im required to take for architecture

 

I suspect that your school views it as material you have to understand for a degree in architecture.

Anyone who thinks that cos^2(x) means "cos square times x" clearly has no understanding of this material. "cos" by itself has no meaning; to think that you can multiply "cos" by "x" is absurd. While I could explain what it really means, you'd be better off studying your textbook and asking your professor.

 

Physics is like sex. Sure, there are some practical uses but that is not why we do it.
-Richard Feynman

You can replace physics with mathematics. This should give you an idea why some
people like theoretical subjects.

 

ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ

on you getting help but damn this is the the worst thread ever JK