Вычислите: 1) 3/7 + 4/9; 4) 20/21 + 3/7; 7) 2/9 + 5/6; 10) 9/14 - 3/7 + 15/28 2) 8/9 - 7/8; 5) 17/18 - 11/12; 8) 10/21 + 9/14; 11) 1/6 + 1/4 - 1/8; 3) 13/15 - 2/3; 6) 7/16 + 1/6; 9) 7/9 - 4/15; 12) 13/18 - 29/45 + 8/15.

Question

Алсу Баранова

Математика

24 июля, 11:28

Вычислите: 1) 3/7 + 4/9; 4) 20/21 + 3/7; 7) 2/9 + 5/6; 10) 9/14 - 3/7 + 15/28 2) 8/9 - 7/8; 5) 17/18 - 11/12; 8) 10/21 + 9/14; 11) 1/6 + 1/4 - 1/8; 3) 13/15 - 2/3; 6) 7/16 + 1/6; 9) 7/9 - 4/15; 12) 13/18 - 29/45 + 8/15.

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Лев Белов · Answer 1

1) 3/7 + 4/9 = (3*9 + 4*7) / 63 = (27+28) / 63=55/63;

2) 8/9 - 7/8 = (8*8-7*9) / 72 = (64-63) / 72 = 1/72;

3) 13/15 - 2/3 = (13*1 - 2*5) / 15 = (13-10) / 15 = 3/15 = 1/5;

4) 20/21 + 3/7 = (20*1+3*3) / 21 = (20+9) / 21 = 29/21;

5) 17/18 - 11/12 = (17*2 - 11*3) / 36 = (34-33) / 36 = 1/36;

6) 7/16 + 1/6 = (7*3 + 1*8) / 48 = (21+8) / 48 = 29/48;

7) 2/9 + 5/6 = (2*2+5*3) / 18 = (4+15) / 18 = 19/18;

8) 10/21 + 9/14 = (10*2 + 9*3) / 42 = (20+27) / 42 = 47/42;

9) 7/9 - 4/15 = (7*5 - 4*3) / 45 = (35-12) / 45 = 23/45;

10) 9/14 - 3/7 + 15/28 = (9*2 - 3*4 + 15*1) / 28 = (18-12+15) / 28 = 21/28 = 3/4;

11) 1/6 + 1/4 - 1/8 = (1*6+1*4-1*3) / 24 = (6+4-3) / 24 = 7/24;

12) 13/18 - 29/45 + 8/15 = (13*5-29*2+8*6) / 90 = (65-58+48) / 90 = 55/90 = 11/18.