【Jiunndar Yeh】評論
因∠A：∠B：∠C = 5：3：1令∠A = 5a°, ∠B = 3a°, ∠C = a°⇒ 5a° + 3a° + a° = 9a° = 180° a° = 180°/9 = 20°故得∠A = 5 * 20° = 100° > 90° ∠B = 3 * 20° = 60° ∠C = 1 * 20° = 20°⇒ △ABC為鈍角三角型 ...選項(A)正確