Q. An arithmetic sequence is defined as follows:{a1=92ai=ai−1−8Find the sum of the first 28 terms in the sequence.
Identify terms and difference: Identify the first term a1 and the common difference d of the arithmetic sequence.The first term a1 is given as 92, and the common difference d is the amount subtracted from each term to get the next, which is 8.
Use sum formula: Use the formula for the sum of the first n terms of an arithmetic sequence, which is Sn=2n∗(2a1+(n−1)d), where Sn is the sum of the first n terms, a1 is the first term, d is the common difference, and n is the number of terms.
Plug values and calculate: Plug the values into the formula to find the sum of the first 28 terms.We have n=28, a1=92, and d=−8 (since the sequence is decreasing).S28=228×(2×92+(28−1)×(−8))
Simplify expression: Simplify the expression inside the parentheses first.2×92=184(28−1)×(−8)=27×(−8)=−216Now add these two results: 184+(−216)=−32
Calculate sum: Now, calculate the sum using the simplified expression.S28=228×(−32)S28=14×(−32)S28=−448
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