Question

an AP.
21 ,18
– – to be taken to find
How many terms of
the sum of 54.​

Answer 1

Answer:

Step-by-step explanation:we know an= a+(n-1)d and sn=n/2[2a+(n-1)d]

NOW we will get the answer from these two expressions

54=n/2[42+(n-1)3]

108=42n+3n^2-3n

108=39n+3n^2

We finding roots for quadratic expression is -b+or-(b^2-4ac)^^1/2/2a

5/2 terms are required