Question

12. In an AP of 20 terms common difference is 6 and and S20 is 1040. Find its first term.
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Answer 1

Answer:

first term = -5

Step-by-step explanation:

Sn = n/2(2a + (n-1)d)

$1040 = \frac{20}{2} (2a + (20 - 1)6) \\ 1040 = 10(2a + 19(6)) \\ 1040 = 10(2a + 114) \\ \frac{1040}{10} = 2a + 114 \\ 104 = 2a + 114 \\ 2a = 104 - 114 \\ 2a = - 10 \\ a = \frac{ - 10}{2} \\ a = - 5$

first term is -5

hope you get your answer