Question

Find the sum of the AP
-5, + -1 + 3, + 7-------- 91​

Answer 1

Answer:

1075

Step by Step Explanation

An = a + (n-1)d

here a= -5

d = 4

An = 91 putting values in above equation we get n-1 = 24,

n = 25

Now for its Sum,

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

putting all the values in equation

Sn = 25/2{-10+(25-1)4}

Sn = 25/2{ 86}

Sn = 25×43

Sn = 1075