allerySum of the first n terms of an AP equals
Aa + (n - 1) d as the formula
Bn * (a + (n - 1) d) directly
Cn/2 * (2 a + (n - 1) d)
Da * (1 - d^n) / (1 - d)
Answer & Solution
Correct answer: C. n/2 * (2 a + (n - 1) d)
1. The last term is a + (n - 1) d.
2. Average of first and last is (2 a + (n - 1) d) / 2.
3. Multiply by n to get S_n = n/2 * (2 a + (n - 1) d).
4. So option A is correct.
_Source: Selina Concise Mathematics Class 10, Ch on Arithmetic Progression (Mistral OCR'd PDF), section on sum_
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