Jawabanmu

2014-09-06T15:11:17+07:00
15a + 7b - 5c + (-11a - 12b + 13d)
= 15a + 7b - 5c - 11a - 12b +13d
= 15a - 11a + 7b - 12b - 5c + 13d
= 4a - 5b - 5c +13d
2014-09-06T15:17:54+07:00
15a+7b-5c+(-11a)-12b+13d
15a+7b-5c-11a-12b+13d
15a-11a+7b-12b-5c+13d
4a-5b-5c+13d
1 5 1