Ответ и объяснение:
1 2/3-5/14+(13/4-1/12)-4/21=4 2/7=4,285714285714286
1) 13/4-1/12=13*3/4*3-1*1/12*1=39/12-1/12 = 39-1/12= 38/12=19*2/6*2=19/6=3*6+1/6=3 1/6
2) 1 2/3-5/14=2+1*3/3-5/14=5/3-5/14=5*14/3*14-5*3/14*3=70/42-15/42=70-15/42=55/42=1*42+13/42=1 13/42
3) 1 13/42+3 1/6=4+13/42+1/6=4+13*1/42*1+1*7/6*7= 4+13/42+7/42=4+13+7/42=4+20/42=4+10*2/21*2=4+10/21=4 10/21
4) 4 10/21-4/21=10+4*21/21-4/21=94/21-4/21=94-4/21=90/21=30*3\7*3=30/7=4*7+2/7 =4 2/7=4,285714285714286