8. Sequences and Series
medium

यदि किसी समांतर श्रेणी के $n$ पदों का योग $n P +\frac{1}{2} n(n-1) Q$, है, जहाँ $P$ तथा $Q$ अचर हो तो सार्व अंतर ज्ञात कीजिए।

A

$Q$

B

$Q$

C

$Q$

D

$Q$

Solution

Let $a_{1}, a_{2}, \ldots a_{n}$ be the given $\mathrm{A.P.}$ Then

${S_n} = {a_1} + {a_2} + {a_3} +  \ldots  + {a_{n – 1}} + {a_n} = nP + \frac{1}{2}n(n – 1)Q$

Therefore     $S_{1}=a_{1}=P, S_{2}=a_{1}+a_{2}=2 P+Q$

So that        $a_{2}= S _{2}- S _{1}= P + Q$

Hence, the common difference is given by $d=a_{2}-a_{1}=(P+Q)-P=Q$

Standard 11
Mathematics

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