Question

Nilai a,b dan c berturut – turut yang memenuhi sistem persamaan dibawah ini
-a + 7b + c = -6
4a + b -2c = 1
3a – 2b + 4c = 20

Gunakan metode subtitusi

Answer 1

-a + 7b + c = -6
c = a - 7b - 6 
,
c = a - 7b - 6  sub ke 4a + b - 2c =1
4a + b - 2(a - 7b - 6) = 1
4a + b - 2a + 14b + 12 = 1
2a + 15b = -11
2a = -11 - 15b 
a = -11/2  - 15/2 b ...(1)
.
c = a - 7b -c sub ke 3a - 2b + 4c = 20
3a - 2b + 4(a - 7b - 6) = 20
3a - 2b + 4a - 28b - 24 = 20
7a - 30 b = 44 ,,,(2)
.
(1) subke (2)
7 (-11/2 - 15/2 b ) - 30 b = 44
-77/2 - 105/2 b - 30b = 44
-77 - 105 b - 60b = 88
-165 b = 88+77
-165 b = 165
b = -1
.
b = 1 sub ke 7a - 30b = 44
7a - 30(-1) = 44
7a+ 30 = 44
7a = 44 - 30
7a = 14
a = 2 

c = a - 7b - 6
c = 2 -7(-1) - 6
c = 2 +7 - 6
c = 3

a, b, c = 2, -1, 3