Sum of first 25 terms of an AP
An arithmetic progression (AP) is a sequence of numbers in which each term is obtained by adding a constant difference to the preceding term. In this problem, we are given an AP whose nth term is 1-4n. We need to find the sum of the first 25 terms of this AP.
Finding the common difference
To find the common difference of the given AP, we need to subtract the (n-1)th term from the nth term.
nth term = 1-4n
(n-1)th term = 1-4(n-1) = 5-4n
Common difference = nth term - (n-1)th term
Common difference = (1-4n) - (5-4n) = -4
Finding the sum of the first 25 terms
To find the sum of the first 25 terms, we can use the formula:
Sum of n terms = (n/2) x [2a + (n-1)d]
where a is the first term, d is the common difference and n is the number of terms.
Here, a = 1, d = -4 and n = 25.
Sum of 25 terms = (25/2) x [2(1) + (25-1)(-4)]
Sum of 25 terms = (25/2) x [-96]
Sum of 25 terms = -1200
Final answer
The sum of the first 25 terms of the given AP is -1200.