3olotaya ( 3 1/ 14 - 2 5/21)*(2,7-2,1)=1/2
21 = 3 · 7
14 = 2 · 7
НОК (14; 21) = 3 · 7 · 2 = 42

1) 3ц1/14-2ц5/21=3ц3/42-2ц10/42=2ц45/42-2ц10/42=35/42
2) 2,7-2,1=0,6
3)35/42*0,6=35/42 * 6/10=35*6 / 42*10=7*1/7*2=7/14=1/2