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Rezolvati va rog.
Calculati 5a-11b+21c,stiind ca 2a+b-3c=15 si a-4b+8c=25 unde a,b,c apartin lui R


Răspuns :

a-4b+8c=25
3(a-4b+8c)=3*25
3a-12b+24c=75
(2a+b-3c)+(3a-12b+24c)=15+75
5a-11b+21c=90