(Y 27 -Y21 - Y15) : ( 3 -Y7 -Y5) = (Y3*Y9 - Y3*Y7 -Y3*Y5) : (3 -Y7-Y5) =
= Y3(3-Y7-Y5) : (3-Y7-Y5) = Y3
(Y 27 -Y21 - Y15) : ( 3 -Y7 -Y5) = (Y3*Y9 - Y3*Y7 -Y3*Y5) : (3 -Y7-Y5) =
= Y3(3-Y7-Y5) : (3-Y7-Y5) = Y3