Răspuns :
a+b=10 si b+c=12 calculeaza 3·a+7·b+4·c
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( a+b=10 )×3 ⇒3a+3b=30 (1)
( b+c=12 ) ×4 ⇒4b+4c=48 (2)
Adunam relatiile (1) si (2) si ⇒
3a+3b+4b+4c=30+48⇒ 3a+7b+4c=78
a+b=10 si b+c=12 calculeaza 3·a+7·b+4·c
_________________________________
( a+b=10 )×3 ⇒3a+3b=30 (1)
( b+c=12 ) ×4 ⇒4b+4c=48 (2)
Adunam relatiile (1) si (2) si ⇒
3a+3b+4b+4c=30+48⇒ 3a+7b+4c=78