$$1,2,3,4,...$$  

$$2,\ 4,\ 6,\ ...,\ 100000$$  

$$a_n=\frac{n}{n+1}$$ เมื่อ n เป็นจำนวนเต็มบวก

$$a_n=2n\ -\ 1\$$ เมื่อ $$n\in\left\{1,2,3,...\right\}$$  

5, 8, 11, 14, 17

5, 7, 9, 15,  18

5, 7, 11, 19, 35

5, 7, 9, 11, 19

1, 4, 5, 7, 8, ...

2, 4, 6, 8, 10, ...

-1, 2, -3, 4, -5, ...

10, 11, 12, 15, ...

5

10

12.5

20

1 , 2 , 3 , ... , 20

1 , 2 , 3 , ...

-5 , -3 , -1 , ... , 5

0 , 5 , 10 , 15 , ... , 65

$$a_n\ =\ a_1\ r^{\ n\ -1}$$  

$$\ a_{n\ }=\ a_1+\left(n-1\right)d$$  

$$a_1\ =\ a_n\ r^{\ n}$$  

ไม่มีข้อถูก

1, 4, 7, 10, 13,...

2, 4, 8, 16, 32, ...

5, 10, 15, 30, 50,...

0, 2, 4, 6, 8, ...

-64

64

-128

128

4

5

6

7

$$S_n=\frac{n}{2}\left(a_1+a_n\right)$$  

$$S_n=\frac{n}{2}\left[a_1+\left(n-1\right)d\right]$$  

$$S_n=\frac{a_1\left(1-r^n\right)}{1-r}$$  

$$S_n=\frac{a_1-a_nr}{1-r}$$  

40 วัน

50 วัน

60 วัน

70 วัน

14,985

14,652

15,318

15,651

54

55

56

57

$$s_n=\frac{a_1\left(1-r^n\right)}{\left(1-r\right)}$$

$$s_n\ =\frac{a_1\left(1-r\right)^n}{\left(1-r\right)}$$

$$s_n=\frac{a_1\left(r^{ }-1\right)}{\left(r-1\right)}$$

$$s_n=\frac{a_1\left(r^n-1\right)}{1-r}$$

$$1+(-1)+1+(-1)+...$$  

$$4+2+1+\frac{1}{2}+...$$  

$$1+3+5+7+...$$  

$$1+(-3)+9+...+729$$  

111

121

131

141

$$\frac{511}{256}$$  

$$\frac{512}{256}$$  

$$\frac{1,023}{512}$$  

$$\frac{1,024}{512}$$  

22,767 บาท

32,767 บาท

22,667 บาท

32,667 บาท

1,023

-1,023

3,069

-3,069