Question

how many terms of an ap 1,9,17,25 must be given a sum of 644

Answer 1

Answer:

a=1

d=9-1=8

Sn=644

n=?

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

644=n/2[2*1+(n-1)8]

644*2=n(2+8n-8)

1288=2n+8n²-8n

1288=8n²-6n

8n²-6n-1288=0

or 4n²-3n-644=0///////now i can not solve

further you can solve

Step-by-step explanation: