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Daca a+b=20 si b+c=33 cat face 3a+7b+4c plz repede

Răspuns :

a + b = 20   si   b + c = 33

3 a + 7 b + 4 c = 192

= 3 a + 3 b + 4 b + 4 c =

= 3 × ( a + b ) + 4 × ( b + c ) =

= 3 × 20 + 4 × 33 =

= 60 + 132 =

= 192

3a+7b+4c=3a+3b+4b+4c=3(a+b)+4(b+c)=3x20+4x33=60+132=192