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Daca a+b=5 si b+c=7 atunci 2a+5b+3c=?

Răspuns :

2(a+b)=10
2a+2b=10
3b+3c=7x3=21
2a+2b+3b+3c=10+21
2a+5b+3c=31
a+b=5
b+c=7
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2a+5b+3c=?
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2(a+b)=10
2a+2b=10
3b+3c=7*3
3b+3c=21
2a+2b+3b+3c=10+21
2a+5b+3c=31