-3x(-2x^2+x-3)=6x^3-3x^2+9x.
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(5/8у - 2 3/4) * 8 = 3
5/8у - 2 3/4 = 3 : 8 = 3/8
5/8у = 3/8 + 2 3/4 = 3/8 + 2 6/8 = 2 9/8 = 25/8
у = 25/8 : 5/8 = 25/8 * 8/5 = 25/5 = 5
у = 5
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Проверка:
(5/8 * 5 - 2 3/4) * 8 = 3
(25/8 - 11/4) * 8 = 3
(25/8 - 22/8) * 8 = 3
3/8 * 8 = 3
3 = 3
3 4/7 + 1 2/3 = 25/7 + 5/3 =(25 × 3 + 5 × 7)/21 = 75/21 + 35/21 = 110/21 = 5 5/21