Jawaban:

12) 2x - 3y = 7 ... pers 1 | ×3

3x + 2y = 4 ... pers 2 | ×2

_________

6x - 9y = 21

6x + 4y = 8

_________ -

-13y = 13

y = 13/-13 = -1

2x - 3y = 7

2x - 3(-1) = 7

2x + 3 = 7

2x = 7 - 3

2x = 4

x = 4/2 = 2

x - y = 2 - (-1) = 2 + 1 = 3 [ D ]

13) keliling = 2(panjang + lebar)

30 = 2((x + 1) + x)

30 = 2(2x + 1)

30 = 4x + 2

30 - 2 = 4x

28 = 4x

x = 28/4 = 7

panjang = x + 1 = 7 + 1 = 8 cm

lebar = 7 cm

luas = p × l = 8 × 7 = 56 cm2 [ C ]

14) 3x - y = 15 ... pers 1 => -y = 15 - 3x

=> y = -15 + 3x ... pers 3

subs pers 3 ke pers 2

x + 3y = 3 ... pers 2

x + 3(-15 + 3x) = 3

x - 45 + 9x = 3

10x = 3 + 45

x = 48/10 = 4,8

subs x ke pers 3

y = -15 + 3(4,8) = -15 + 14,4 = -0,6

x - 2y = 4,8 - 2(-0,6) = 4,8 + 1,2 = 6 [ B ]