`cos(pi/4-x)cos(pi/4-y)-sin(pi/4-x)sin(pi/4-y)=sin(x+y)`

1.	`cos(pi/4-x)cos(pi/4-y)-sin(pi/4-x)sin(pi/4-y)=sin(x+y)`
Answer» LHS. `=cos(pi/4-x) cos(pi/4-y)-sin(pi/4-x)sin(pi/4-y)` `=cos[pi/2-(x+y)]` `=sin(x+y)`= RHS Hence Proved.

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