only genius can ans. this .....no spammimg....
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only genius can ans. this .....no spammimg....
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Here is ur answer,
Sum of 9 terms => 81.
Sum of 20 terms => 400.
Multiply the equation (1) by 2.
=> 2a+8d = 18.......... (3)
Subtracting eq (3) from (2).
=> 2a+19d-2a-8d =40-18.
=> 11d =22.
=> d=2.
Substitute the value of d in eq (1).
=> a+4d = 9.
=> a+4 (2) =9.
=> a =9-8 =1.
Sum of first 15 terms
=> 15×30/2.
=> 15×15
=> 225.
So, The first term is 1.
Common difference => 2.
Sum of first 15 terms => 225.
:-(Hope it helps u. 《《 VIDYA》》