Misalkan, panjang diagonal 1 (d1) qdalah a, maka panjang diagonal 2 (d2) adalah (3/4)a

Luas belah ketupat = 1/2 × d1 × d2

864 cm² = 1/2 × a × (3/4)a

864 cm² × 2 = a × 3a/4

1.728 cm² = 3a²/4

1.728 cm² × 4 = 3a²

6.912 cm² = 3a²

6.912 cm² / 3 = a²

2.304 cm² = a²

√(2.304 cm²) = a

48 cm = a

Panjang d1 = a = 48 cm

Panjang d2 = 3a/4 = 3(48)/4 = 36 cm

Sisi nya kita cari pakai Phytagoras.

s² = (24 cm)² + (18 cm)²

s² = 576 cm² + 324 cm²

s² = 900 cm²

s = √(900 cm²)

s = 30 cm

Keliling = 4 × s

= 4 × 30 cm

= 120 cm (C.)