kerjakan no 13 dan 14 dengan cara

13.)
panjang sisi sama kaki :
12 + 6 = 18
28 - 18 = 10 ÷ 2 = 5 dm

12 - 6 = 6 ÷ 2 = 3

tinggi trapesium :
t² = s² - a²
t² = 5² - 3²
t² = 25 - 9
t² = 16
t = √16
t = 4 dm

Luas trapesium :
= (a + b) × t / 2
= (6 + 12) × 4 / 2
= 18 × 4 / 2
= 36 dm² (b)

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14.)
Luas = (a + b) × t / 2
288 = (3x + 6x) × 4x / 2
288 = 9x × 4x / 2
576 = 36x²
x² = 16
x = √16
x = 4

s² = a² + t²
s² = (3x)² + (4x)²
s² = (3 × 4)² + (4 × 4)²
s² = 12² + 16²
s² = 144 + 256
s² = 400
s = √400
s = 20 cm

Keliling = 3x + 4x + 6x + 20
= (3 × 4) + (4 × 4) + (6 × 4) + 20
= 12 + 16 + 24 + 20
= 72 cm (c)