Sin a * cos b + sin b * cos a = sin(a+b)
=> Sin(pi/12)cos(11pi/12) + cos (pi/12) sin (11pi/12) = sin(pi/12 + 11pi/12) = sin pi = 0
1) X² - 3XY = X * ( X - 3Y )
2) X² / ( X * ( X - 3Y )) = X / ( X - 3Y )
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3) X^2 - 9Y^2 = ( X - 3Y )*( X + 3Y )
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[ X / ( X - 3Y ) ] * [ (( X - 3Y )*( X + 3Y ) ) / X ] = X + 3Y
ОТВЕТ Х + 3Y