Question

cum sa rezolv exercitiul:
x+y=17
y-z=4
.................
x+2y-z=?
x+z=?

Answer 1

(x+y)+(y-z)=x+2y -z= 17+4=21
x+y-(y-z)=x+y-y+z=x+z=17-4=13

Answer 2

x+y=17=> x=17-y
y-z=4=>y=4-z 
daca y=4-z =>x=17-4-z
                     x=13-z

x+2y-z=13-z+2(4-z)-z=13-z+8-2z-z=21-4z
x+z=13-z+z=13