Question

1 Fie a,b,c, apartine lui R astfel incat a+b=2. b+c=5 si c+a=11. calculati a b c ,a+b+c

Answer 1

a+b=2
b+c=5
c+a=11
(a+b)+(b+c)+(c+a)=2+5+11
2a+2b+2c=18
a+b+c=9
(a+b+c)-(b+c)=9-5
a=4
b=-2
c=7

Answer 2

a+b=2
b+c=5
c+a=11
abc=?
a+b+c=?
a+b+b+c+c+a=2+5+11=18
2a+2b+2c=18
2(a+b+c)=18
a+b+c=18:2
a+b+c=9
2+c=9⇒c=7
b+7=5⇒b=-2
7+a=11⇒a=4