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First term = a =18
Common difference = d = −18=−52
a n=−47
Using formula a n=a+(n−1)d, to find nth term of arithmetic progression, we get
−47 = 18+(n−1)[−52] = 36−5n+52
⇒−94 = 36 − 5n+5
⇒5n = 135
⇒n= =27
Therefore, there are 27 terms in the given arithmetic progression.
Example 5- The sum of three number in A.P. is 27. The product of first and last is
56. Find the number?
Solution- Let the numbers are in AP be a - d, a, a + d
The sum of three number in A.P. is 27.
a - d + a + a + d = 27
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