Question

Lebar suatu persegi pnjang sepertiga dari panjangnya.jika keliling persegi panjang 56cm, maka luas persegi panjang tersebut adlah
a.126
b.147
c.243
d.588

Answer 1

Lebar = x
Panjang = 3x
Keliling = 2 (p+l)
56 = 2 (p+l)
(p+l) = 56/2 = 28 cm
x + 3x = 28
4x = 28
x = 28/4
x = 7
jadi lebar = x  = 7 cm
panjang = 3x = 3 x 7 = 21 cm
Maka luas = panjang x lebar = 21 x 7 = 147 (b)

Answer 2

L = 1/3p
k = 56
k = 2(p+l)
56=2(p + 1/3p)
56/2=3p/3+ 1p/3
28 = 4p/3
28 × 3 = 4p
84 = 4p
p = 84/4
p = 21

luas = p × l
= 21 × 1/3(21)
= 21 × 7
=147 (B)