hasil determinan a+b+c= 30,6a-12b-3c=-45,4a+5b-6c=80

A + b + c = 30 | ×3
6a-12b-3c =-45 | ×1

3a + 3b + 3c =90
6a - 12b - 3c =-45
_____________ +
9a - 9b = 45…

A + b + c = 30| ×6
4a+5b-6c=80 | ×1

6a + 6b + 6c = 180
4a + 5b - 6c = 80
______________+
10a + 11b = 260…

9a - 9b = 45 | ×10
10a - 11b = 260| ×9

90a - 90b = 450
90a - 99b = 2340
______________-
9b = -1890
b = -1890÷9 = 210


9a-9b = 45
9a-1890 = 45
9a = 45 + 1890
a = 1935 ÷ 9 = 215


a+b+c = 30
215 + 210 + c = 30
C = 30 - 215 - 210
c = -395