Question

Jawaban dari Soal UN SMP MTK 2015 yang soalnya :
2/3 x - 1/2y = 6, 1/2x + 1/4y = 2, jika a = x & b = y tentukan a - 2b = ?

Answer 1

2/3 x -1/2 y = 6 |x6| 4x-3y = 36 |x1| 4x-3y = 36
1/2 x + 1/4 y = 2 |x4| 2x+y = 8 |x2| 4x+2y = 16
____________ -
-5y = 20
y = -4

maka : y = -4 -----> 2x+y = 8
2x - 4 = 8
2x = 12 -----> x = 6


jadi, a - 2b = 6 -2.(-4) = 6+8=14

Answer 2

2/3x - 1/2y = 6 [x-2] -4/3x + y =-12
1/2x + 1/4y = 2 [x4] 2x + y = 8  -
                            -3 1/3x = -20
-3 1/3x = -20
10/3x = 20
x = (20 * 3)/10
x = 6

2/3x - 1/2y = 6
2/3(6) - 1/2y = 6
4 - 1/2y = 6
-1/2y = 2
y = -4

jika a = x dan b = y maka a - 2b = 6 - 2(-4) = 6 + 8 = 14