Consider the following sequence:
- Find the sum of 2 + 6 + 10 + 14 + ... + 58.
- A given line of the sequence is as follows: 2 + 6 + 10 + 14 + ... + b = 722 = 2 x c2. Find the value of c.
- Calculate the sum of Line 48 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 58 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 - 258 = Number of numbers x 4 - 2
58 + 2 = Number of numbers x 4
60 = Number of numbers x 4
Number of numbers
= 60 ÷ 4
= 15
Sum of 15 numbers
= 2 x Number of numbers in the string
2
= 2 x 15
2= 2 x 15 x 15
= 2 x 225
= 450
(b)
2 x c
2 = 722
c
2 = 722 ÷ 2
c
2 = 361
c = √361
c = 19
(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
48 =
2 x (
48 + 1)
2 = 2 x 49
2 = 2 x 49 x 49
= 4802
Answer(s): (a) 450; (b) 19; (c) 4802