Question

find the number of terms of AP 54,
51, 48 so that the sum is 513

Answer 1

Answer:

Step-by-step explanation:

Given : a= 54

d = 51-54= -3

Sn =513

To find : n= ?

Solution:

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

513= n/2 [2×54+(n-1) -3]

513×2= n [108-3n+3]

1026= 111n-3n sq

3n sq -111n+1026=0

n2 - 37n + 342 = 0 {divide by 3}

Splitting the middleterm

(n - 18)×(n - 19) = 0

n = 18, 19

Hence, number of terms is either 18 or 19

Hope it helps you!

Answer 2

Please refer the attachment

Required Answer is 18 or 19