3x-4y=-21suy ra3x=4y-21
3x=3y-21+y;x=(3y-21+y):3;x=y-7+y:3
Vì x,y là số nguyên dương nhỏ hơn 10 nên y chia hết cho 3 suy ra y thuộc {6;9}.
Với y=6 thì x = 1
Với y =9 thì x = 5
Làm chẳng ra gì . Bố méo thèm chép.
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y=6 và x=1
y=9 và x=5
các bạn nhớ k cho mình nha mình đang bị âm điểm ^_^
3x+7=28
3x =28-7
3x =21
x =21:3
x =7