Jawab:

12.

Pada belah ketupat:

(1/2 diagonal₁)² + (1/2 diagonal₂)² = (panjang sisi)²

(1/2 d₁)² + (1/2 d₂)² = s²

(1/2 x 6)² + (1/2 d₂)² = 5²

3² + (1/2 d₂)² = 5²

9 + (1/2 d₂)² = 25

(1/2 d₂)² = 25 - 9 = 16

1/2 d₂ = √16 = 4

Panjang diagonal₂ = 4 x 2 = 8

Luas belah ketupat = 1/2 x diagonal 1 x diagonal 2

L = 1/2 x d₁ x d₂

L = 1/2 x 6 x 8 = 3 x 8 = 24 cm²

13.

(1/2 d₁)² + (1/2 d₂)² = s²

(1/2 x 16)² + (1/2 x 12)² = s²

8² + 6² = s²

64 + 36 = s²

100 = s²

s = panjang sisi = √100 = 10 cm

Keliling = 4 x s

             = 4 x 10

             = 40 cm