Question

Daca a+b=36,b+c=57 si a+c+=51,calculati c-a-b.

Answer 1

a+b=36
b+c=57
a+c=51     adunam cele trei relatii si rezulta 
_________
2a+2b+2c=144 /:2  acum impartim relatia la 2 => a+b+c=72

36+c=72
c=72-36
c=36

a+57=72
a=72-57
a=15

51+b=72
b=72-51
b=21

c-a-b=36-15-21=0

Answer 2

a + b = 36
b + c = 57
a + c = 51
c - (a + b) = 
= c - 36
c = 36
a + 36 = 51
a = 51 - 36
a = 15
15 + b = 36
b = 36 - 15
b = 21
c - a - b = 36 - 15 - 21 = 0