Question

The sum of n terms of 1.4, 3.7, 5.10 ……. Is (a) (n/2)(4n²+5n–1) (b) n(4n²+5n–1) (c) (n/2)(4n²–5n–1) (d) None

Answer 1

Step-by-step explanation:

$a1 = 1.4 \\ d = a2 - a1 = 3.7 - 1.4 = 2.3 \\ sum = \frac{n}{2} (2a + (n - 1)d) \\ sum = \frac{n}{2} (2 \times 1.4 + (n - 1)2.3 )\\ sum = \frac{n}{2} (2.8 + 2.3n - 2.3) \\ = \frac{n}{2} (0.5 + 2.3n)$