Question

3+9+15+21.....+63=X then the value of X us​

Answer 1

It is an A.p

of

d=6

a=3

By using the sum of terms of an AP formula we get ,

Sn=n/2(a+l)

Now Frist we have to find n .

An = a+(n-1)d

63=3+(n-1)6

n=10

Now by substituting the value of n .

we get,

Sn=10/2(3+63)

= 5×66= 320.

hope it is helpful to you.

Answer 2

Heya!!

Given series is in A.P becoz Common difference is same

x = n/2 { a + An }

Where a is ist term , n is Number of terms and An is nth term.

An = a + ( n -1 )d

=>

63 = 3 + ( n -1 ) 6

=>

60/6 = ( n -1 )

=>

( n -1 ) = 10

=>

n = 11

So, then number of terms is 11

x = 11/2 { 63 + 3}

x = ( 66 × 11 )/2

x = 363.