How many terms of an A.P. 9, 17, 25, ... must be taken to give a sum of 636 ?
Answers
Answer:
12
Step-by-step explanation:
Let the number of terms required to make the sum of 636 be n and the common difference be d.
Given Arithmetic Progression: 9, 17, 25 ....
First term = a = 9
Second term = a + d = 17
Common difference = d = a + d - a = 17 - 9 = 8
From the indentities of arithmetic progressions, we know: -
, where is the sum of the first term to the nth term of the AP, a is the first term, d is the common difference and n is the number of terms of AP.
In the given Question, sum of APs is 636.
Therefore,
= > 4n² + 5n - 636 = 0
= > 4n² + ( 53 - 48 )n - 636 = 0
= > 4n² + 53n - 48n - 636 = 0
= > 4n² - 48n + 53n - 636 = 0
= > 4n( n - 12 ) + 53( n - 12 ) = 0
= > ( n - 12 )( 4n + 53 ) = 0
By Zero Product Rule,
= > n - 12 = 0
= > n = 12
Hence,
Number of terms of the AP [ 9 , 17 , 25 ] which are required to make the sum of 636 is 12.