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tinggi trapesium
t² = 17² - (20-5)²
t² = 289 - 225
t² = 64
t = √64
t = 8 cm

V = L alas × tinggi
V = (1/2×(a+b) × t) × tinggi
V = (1/2×(20+5) × 8) × 20
V = (1/2 × 25 × 8) × 20
V = 100 × 20
V = 2000 cm³