Jawabanmu

2014-09-09T16:37:57+07:00
(15a+7b-5c) - (-11a-12b+13c) = 15a + 11a + 7b + 12b - 5c -13c = 26a + 19b - 18c
2014-09-09T16:38:22+07:00
15a + 7b - 5c + 11a + 12 b - 13c
= 26a + 19b - 18c