prediksi soal UN matematika 2016/2017 tanah pak mamad berbentuk persegi panjang dg keliling 42 m . jika panjang tanah (3x - 2) m dan lebar tanah (x+3) m . maka

kel = 2x((3x-2)m+(x+3)m)
42m = 2x(4x+1)m
42m = 8x+2m
42m-2m =8x
40m = 8x
5m = x

panjang = 3x-2m = 3.5m-2 = 15-m2 = 13m
lebar = x+3m = 5m+3 = 8m

luas = p x l = 13m x 8m = 104m² (a)

p = (3x - 2) m
l = (x + 3) m

Keliling = 42 m
2p + 2l = 42
2 (3x - 2) + 2 (x + 3) = 42
6x - 4 + 2x + 6 = 42
6x + 2x - 4 + 6 = 42
8x + 2 = 42
8x = 42 - 2
8x = 40
x = 40/8
x = 5 m

p = 3x - 2 m
p = 3 (5) - 2
p = 15 - 2
p = 13 m

l = x + 3 m
l = 5 + 3
l = 8 m

Luas tanah Pak Mamad
= p x l
= 13 x 8
= 104 m² (Opsi A)