Jika keliling persegi panjang 44 cm, luas persegi panjang tersebut yaitu ….
Pembahasan:
Persegi panjang: panjang p = 3x + 4
lebar ℓ = 2x + 3
Keliling:
K = 44 cm
2(p + ℓ) = K
2(3x + 4 + 2x + 3) = 44
2(5x + 7) = 44
10x + 14 = 44
10x = 44 – 14
10x = 30
x = 3
p = 3x + 4 = 3 × 3 + 4 = 13 cm
ℓ = 2x + 3 = 2 × 3 + 3 = 9 cm
Luas persegi panjang = p × ℓ = 13 × 9 = 117 cm².