Đáp án:1)a.
2/7+4/7=(2+4)/7=6/7
6/7-2/7=(6-2)/7=4/7
4/7+2/7=(4+2)/7=6/7
b.
-1/3+5/12=4/12+5/12=9/12=3/4
-9/12-1/3=9/12-4/12=5/12
-9/12-5/12=(9-5)/12=4/12=1/3
-5/12+1/3=5/12+4/12=(5+4)/12=9/12=3/4
2)a.
-2/7+3/5=10/35+21/35=(10+21)/35=31/35
-31/35-2/7=31/35-10/35=(31-10)/35=21/35=3/5
-31/35-3/5=31/35-21/35=(31-21)/35=10/35=2/7
-3/5+2/7=21/35+10/35=(21+10)/35=31/35
b.
-3/4+1/6=18/24+4/24=(18+4)/24=22/24=11/12
-11/12-3/4=11/12-9/12=(11-9)/12=2/12=1/6
-11/12-1/6=11/12-2/12=(11-2)/12=9/12=3/4
-1/6+3/4=4/24+18/24=(4+18)/24=22/24=11/12
3) a. b. 6/7-x=2/3 c. x-1/2=1/4
2/9+x=1 x=6/7-2/3 x =1/4+1/2
x=1-2/9 x=18/21-14/21 x =1/4+2/4
x=9/9-2/9 x=4/21 x =3/4
x=7/9
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