Sin (50 + A) = sin50 cosA + cos50 Sin A

Cos (40 - A) = cos40 CosA + sin 40 Sin A

so

Sin (50+A) - Cos (40 - A) = Cos A ( Sin 50-Cos40) + SinA(Cos 50 - Sin40)

Sin50 = cos (90-50) = cos 40 and similarly

Cos50 = sin 40

or

Sin50 - Cos40 = 0

Cos50 - Sin40 = 0

So Answer is **ZERO**