1) SIN X+SIN Y=SIN X -SIN Y.

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вопрос

This equation is not true. In general, sin(x) + sin(y) is not equal to sin(x) - sin(y).

A correct equation involving sine functions might be:

sin(x) + sin(y) = 2sin((x+y)/2)cos((x-y)/2)

or

sin(x) - sin(y) = 2cos((x+y)/2)sin((x-y)/2)

Both of these equations involve trigonometric identities relating to the sum and difference of angles for sine and cosine functions.