Consider the following sequence:
- Find the sum of 2 + 6 + 10 + 14 + ... + 70.
- A given line of the sequence is as follows: 2 + 6 + 10 + 14 + ... + d = 242 = 2 x e2. Find the value of e.
- Calculate the sum of Line 44 if the pattern for the sum of the lines is as follows:-
Line 1: 8
Line 2: 8 + 10
Line 3: 8 + 10 + 12
(a)
Sum of 1 number:
2 =
2 x
12Sum of 2 numbers:
2 + 6 = 8 =
2 x
22Sum of 3 numbers:
2 + 6 + 10 = 18 =
2 x
32 Sum of 4 numbers:
2 + 6 + 10 + 14 = 32 =
2 x
42
Formula:
Sum of numbers =
2 x
Number of numbers in the string2
To find out how many numbers are in the string if 70 is the last number.
Last number in sum of 1 number:
2 = 1 x 4 - 2
Last number in sum of 2 numbers:
6 = 2 x 4 - 2
Last number in sum of 3 numbers:
10 = 3 x 4 - 2
Last number in sum of 4 numbers:
14 = 4 x 4 - 2
Formula:
Last number =
Number of numbers in the string x 4 - 270 = Number of numbers x 4 - 2
70 + 2 = Number of numbers x 4
72 = Number of numbers x 4
Number of numbers
= 72 ÷ 4
= 18
Sum of 18 numbers
= 2 x Number of numbers in the string
2
= 2 x 18
2= 2 x 18 x 18
= 2 x 324
= 648
(b)
2 x e
2 = 242
e
2 = 242 ÷ 2
e
2 = 121
e = √121
e = 11
(c)
Pattern for the sum of the lines
Line
1: 8 =
2 x (
1 + 1)
2 Line
2: 8 + 10 = 18 =
2 x (
2 + 1)
2 Line
3: 8 + 10 + 12 = 32 =
2 x (
3 + 1)
2 Formula:
Sum of Line Number =
2 x (
Line Number + 1)
2Sum of Line
44 =
2 x (
44 + 1)
2 = 2 x 45
2 = 2 x 45 x 45
= 4050
Answer(s): (a) 648; (b) 11; (c) 4050