The sum of the first n terms of the arithmetic ... - JAMB Mathematics 2009 Question
The sum of the first n terms of the arithmetic progression 5, 11, 17, 23, 29, 35,... is
A
n(3n - 0.5)
B
n(3n + 2)
C
n(3n + 2.5)
D
n(3n + 5)
correct option: b
Tn = \(\frac{1}{2}\)n(2a + (n - 1)d)
= \(\frac{1}{2}\)n(2 x 5 + (n - 1) 6
= \(\frac{1}{2}\)n(10 + 6n - 6)
= n\(\frac{1}{2}\)(6n + 4)
= n(3n + 2)
= \(\frac{1}{2}\)n(2 x 5 + (n - 1) 6
= \(\frac{1}{2}\)n(10 + 6n - 6)
= n\(\frac{1}{2}\)(6n + 4)
= n(3n + 2)
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