Question

Find the sum of the first 19 terms of the AP, whose nth term is given by tn=7-4 n

Answer 1

Answer:

-627

Step-by-step explanation:

$t_{n} = 7 - 4n=7 - 4n +4 - 4=3 + (n-1)(-4)$

This represents AP with first term 3 and common difference -4

$S_n = \frac{n}{2}[2a + (n-1)d]\\\\S_{19} = \frac{19}{2}[6 + 18(-4)]=19[3 -36]=19[-33]=-627$