Răspunsuri

2014-08-03T09:12:55+03:00
X+y=90

x=90-y

y+z=21

y=21-z

x=90-21+z= 69+z

x+z=75

69+z+z=75

2z=75-69

2z=6

z=3

x=69+3=72

y=21-3=18
cum ai ajuns aici
x=90-21+z= 69+z
deci x=90-y si y=21-z
x=90-(21-z)= 90-21+z
x=69+z