13. 已知為整數,求a的最小正整數為______________。
20. If = 13, what is the value of ? (A) 312; (B) 156; (C) 104; (D) 52.
18. What is a for making the equation = 2 hold? (A) 1000; (B) 9; (C) 300; (D) 600.