Question

the common difference of an ap is -2 find its sum if its first term is 100 and the last term is minus 10​

Answer 1

Answer:

A =100

D=-2

An=-10

An=a+(n-1)d

-10=100+(n-1)-2

-10-100=(n-1)-2

-110/-2=(n-1)

55=(n-1)

N=56

Sn =n/2(a+an)

Sn=56/2(100+(-10))

Sn=28(90)

Sn=2520

The sum is 2520