Question

Daca 2·a+b=5 si 2·b+3·c=7, calculati 4·a+8·b+9·c

Answer 1

2·a+b=5 |*2 =>
4a+2b=10

2·b+3·c=7 |*3
6b+9c=21
calculati 4·a+8·b+9·c ( am descompus 8b sa 2b+6b)

4a+2b+6b+9c=
10+21=31

Answer 2

2a+b=5

2b+3c=7

4a+6b+9c =2(2a+b)+3(2b+3c)=  2*5+3*7=  10+21=31