Math, asked by muhseemuneer, 10 months ago

The sum of first 9 terms of an ap is 351 and the sum of first 20 terms is 1770 find the sum of the first n terms

Answers

Answered by ayushpal071

Answer:

Step-by-step explanation: a =3 and d=9 explainatiom in photo

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muhseemuneer: that was very helpful..... but wat is the the sum of the nth term??

ayushpal071: Put n/2 (2a +(n-1) d, a=3 d=9

ayushpal071: Reply if you want paper explaination

muhseemuneer: so it will be n/2(6a+9n-9)

muhseemuneer: ryt??!!

ayushpal071: No it will 9n²-3n/2

muhseemuneer: ok

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