Question

how many terms of an AP 3,5,7,... must be taken so that the sum is 120?​

Answer 1

Answer:

n=10.

Step-by-step explanation:

a=3.,d=+2.,s=120.,n=?.,an=?

wkt.,

l=a+(n-1)*d....(l is a term)

and sum=n/2(a+l)......(i)

i.e l=3+(n-1)*2

=> l=3+2n-2.....(ii)

putting ii in i..we hv..,

120=n/2(4+2n)

i.e 120=n(2+n)

i.e n^2+2n-120=0

=> on solving................(12n-10n)

= n=10.......,and n= -12(which is nt possible) therefore n=10

Answer 2

Answer:

Step-by-step explanation: