Question

In the A.P. 5,9,13.... find the sum of first 15 terms

Answer 1

Hi there!

First term, a = 5
Common difference, d = 4
No. of terms, n = 15

$S_n$ = n/2 × [ 2a + (n-1)d ]

$S_{15}$ = 15/2 × [2(5) + 14(4) ]

= 15/2 × ( 10 + 56 )

= 15/2 × 66

= 15 × 33

= 495

Hence,
Sum of 15 terms of the following A.P. is 495

[ Thank you! for asking the question.]
Hope it helps!

Answer 2

Answer is in the picture which I have tagged....