Find the sum of the first 20 terms of the sequence -7-3, 1, ......
FURTHER MATHEMATICS
WAEC 2019
Find the sum of the first 20 terms of the sequence -7-3, 1, ......
- A. 620
- B. 660
- C. 690
- D. 1240
Correct Answer: A. 620
Explanation
d = -3 - (-7) = 4
S\(_{20}\) = \(\frac{20}{2}\){2(-7) + (20 - 1) 4}
= 10(- 14 + 76)
= 620
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