Question

the sum of n elements of an

ap is21,23,25,is 384find the numbers of terms and last terms​

Answer 1

Answer:

n=12

last term=43

Step-by-step explanation:

a=21

d=23-21=2

Sn=(n/2){2*21+(n-1)*2}

384=(n/2){42+2n-2}

384=n(20+n)

n²+20n-384=0

n²+32n-12n-384=0

n(n+32)-12(n+32)=0

(n-12)(n+32)=0

n=12 or n!=-32

last term =a+(n-1)*d

= 21+(12-1)*2

=21+22

=43