Question

PLEASE

HELP

ME
!!!!!!!

Answer 1

one trigonometric identity

cos A cos B − sin A sin B = cos ( A+B )

cos (π\4-x) cos (π\4-y)-sin (π\4-x) sin (π\4-y)

Here A = (π\4-x), B= (π\4-y)

= cos [(π\4-x) +(π\4-y)]

= cos [ (π\4+π\4)-(x+y)]

= cos [ (π\2) - (x+y)]

= sin ( x+y )

Since

cos (π\2-x) = sin (x).


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