Math, asked by krishna2133, 1 year ago

find the number of terms in the following arithmetic series 1+2+3+------=1275​

Answers

Answered by waqarsd
5

Answer:

Step-by-step explanation:

given

1 + 2 + 3 + 4 + ................... = 1275

Clearly

1 , 2 , 3 ......... so on are in AP

With a = 1 and d = 1

WKT

\bold{S_n = \frac{n}{2}[2a+(n-1)d]}\\\\\bold{1275=\frac{n}{2}[2+(n-1)]}\\\\\bold{1275=\frac{n}{2}[n+1]}\\\\\bold{2550=n[n+1]}\\\\\bold{n^2+n-2250=0}\\\\\bold{n^2+51n-50n-2550=0}\\\\\bold{n(n+51)-50(n+51)=0}\\\\\bold{(n+51)(n-50)=0}\\\\\bold{n=50}\\\\\bold{n\neq-51\;\;since\;\;n>0 }\\\\

Therefore

There are 50 terms in the following AP

HOPE IT HELPS

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