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a+b=29. b+3×c=21. 3×a+5×b+6×c=?

Răspuns :

a+b=29 inmultim cu 3
3×a+3xb=87

b+3×c=21 inmultim cu 2
2b+6c=42

adunam noile relatii:

3×a+3×b+2×b×6×c=87+42
3×a+5×b+6×c=129