Hi,

I need a little help with an equation I got for math. It is as following:
sin² (x) . Cos² (y) + cos² (x) . Sin² (y) + sin² (x) . Sin² (y) + cos² (x) . Cos² (y) = 1

Now I tried to complete the exercise, but I got stuck. Let me show you what I did.

We know:
sin (x) . Cos (y) + cos (x) . Sin (y) = sin (x + y)

So I thought:
sin² (x) . Cos² (y) + cos² (x) . Sin² (y) = sin² (x + y)

Same for:
sin (x) . Sin (y) + cos (x) . Cos (y) = cos (x - y)

So I also thought:
sin² (x) . Sin² (y) + cos² (x) . Cos² (y)= cos² (x - y)

That gives us:
sin² (x+y) + cos² (x-y)

And that's where I got stuck. So anybody knows where I made an error / knows how I should continue?

Cheers,
A student

Sorry I posted this in the wrong category, feel free to delete this admins.
My apologies.

>thread closed<