Question

The sum of 15 terms of A.P. 3, 6, 9​

Answer 1

Answer:

a=3 d =6-3=3

Step-by-step explanation:

n=15

s15=n/2(2a+(n-1)d)

15/2(2*3+(15-1)3)

15/2(6+14*3)

15/2(6+42)

15/2*48

15*24 =360

Answer 2

The sum of the first 15 numbers is 360.

Step-by-step explanation:

The sequence given to us is 3, 6, 9

To find= The sum of the first 15 numbers

Solution

Now,

The formula for calculating the sum of the first 15 numbers is

= $S_{n}$ = n÷2[2a+(n-1)d]

Here,  $S_{n}$ = sum of n numbers

a= first number

d= difference

From the given sequence, n= 15

d= 6-3= 3

a= 3

Putting the values in the equation we get:

= $S_{n}$ = 15÷2[2×3+(15-1)3]

= $S_{n}$ = 7.5[6+14(3)]

= $S_{n}$ = 7.5×6+42

= $S_{n}$ = 360

Result

Thus, the sum of the first 15 numbers is 360.

(#Spj3)