VÌ UCLN[A:B]->A=20*A1:B=20*B1
VOI [B1,A1]=1 VA A1>B1
MA A+B=60<=>20*A1+20*B1=60
<=>20*[B1+A1]=60
<=>B1+A1=3
VI [B1:A1]=1 NEN TA CO CAC TRUONG HOP SAU:
+TH1:A=1 1=2->A=2*20=40;B1=1->B=1*20=20
+TH2:A1=1->A=1*20=20;B1=2->B=2*20=40
VAY TAT CA CAC CAP [A,B] LA :[20;40],[40;20]