Question

4.
Find the number of terms of the AP: 32, 28, 24, 20, ... of which the sum is 132.
Explain the double answer.​

Answer 1

Answer:

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

here a=32

d=28-32= -4

n=?

Sn=132

132=n/2 (2*32+(n-1)*-4)

264=n(64+4-4n)

264=68n-4n2

4*66=4(17n-n2)

we cut 4 by 4

n2-17n+66=0

n2-11n-6n+66

n(n-11)-6(n-11)

n=6

n=11

hope you will satisfied