Question

find the sum of 15 terms of an AP -3,-5,-7-9
3marks​

Answer 1

Answer:

ye sab answer me 1 me deta tha

Answer 2

Solution:-

Given sequences is

=> - 3 , - 5 , -7 , - 9

=> Common difference ( d ) = a₂ - a₁ = -5 - ( - 3 ) = - 2

=> First term ( a ) = -3

Formula

=> Sₙ = n/2 { 2a + ( n - 1 )d }

To find :- S₁₅

=> S₁₅ = 15/2 { 2 × -3 + ( 15 -1 ) × - 2 }

=> 2S₁₅ = 15{ - 6 + 14 × - 2 }

=> 2S₁₅ = 15 { - 6 - 28 }

=> 2S₁₅ = 15 × - 34

=> 2S₁₅ = - 510

=> S₁₅ = -510/2

=> S₁₅ = -255

Answer

=> Sum of 15terms is -255