Question

Stiind ca x+y=12 si x+z=5, calculati 5x+2z-3z

Answer 1

x+y=12 
x+z=5 => x=5-z
Inlocuim pe x in prima ecuatie.
5-z+y=12 => -z+y=7 => z-y=-7
x=12-y
12-y+z=5
-y=5-z-12
y=7+z
z-7-z=-7 => z=0
z-y=-7 => y=7
x+y=12 => x=5
5x+2y-3z=25+14-0=39
Raspuns final 39