jika a+b=1, a+c=2 dan b+c=7 maka nilai a+b+c adalah?

a+ b = 1
a = 1-b
subtitusikan ke a + c = 2
1 -b + c =2
c-b = 1
c = b+1
shbtitusikan ke b +c=7
b+b+1 = 7
2b =6
b=3

c= b+1
c = 3+1
c = 4

a = 1-b
a = 1-3
a=-2

a+b+c = -2+3+4 = 5