Question

Stiind ca a+b=10 si b+c=20 sa se calculeze 2a+5b+3c.

Answer 1

a+b = 10 / *2 (inmultim aceasta relatie cu 2)
b+c = 20 / *3 (inmultim aceasta relatie cu 3)

Obtinem:
2a+2b = 20
3b+3c = 60
Adunam cele doua relatii si obtinem:
2a+2b+3b+3c = 20+60
2a + 5b + 3c = 80

Answer 2

a+b=10=> a=10-b
b+c=20=> b=20-c } => a=10-(20-c)=10-20+c=-10+c.
inlocuim
2(-10+c) +5(20-c)+3c
-20+2c+100-5c+3c
=80