Hitunglah nilai 2x + 3y jika diketahui: a. 3x - y = 14 2x + 5y =16 b. 4x - 5y = 26 7x + 8y = 10

a) 3x - y = 14 |×5
2x + 5y = 16
maka
15x - 5y = 70
2x + 5y = 16
-------------------(+)
17x = 86
x = 86/17

3x - y = 14 |×2
2x + 5y = 16 |×3
maka
6x - 2y = 28
6x + 15y = 48
---------------------(-)
- 17y = - 20
y = 20/17

nilai 2x + 3y
= 2(86/17) + 3(20/17)
= 172/17 + 60/17
= 232/17
= 13 11/17

b) 4x - 5y = 26 |×8
7x + 8y = 10 |×5
maka
32x - 40y = 208
35x + 40y = 50
------------------------(+)
67x = 258
x = 258/67

4x - 5y = 26 |×7
7x + 8y = 10 |×4
maka
28x - 35y = 182
28x + 32y = 40
-----------------------(-)
- 67y = 142
y = - 142/67

nilai 2x + 3y
= 2(258/67) + 3(-142/67)
= 516/67 - 426/67
= 90/67
= 1 23/67