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CLASS_11_MATHS_SOLUTIONS_NCERT

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Class XI Chapter 9 – Sequences and Series Maths<br />

______________________________________________________________________________<br />

a b c<br />

q r r p p q<br />

p1 qr q1 r p r1 pq<br />

<br />

<br />

qr r p pq<br />

A R A R A R<br />

pr pr q r rq r p pq pr p qr q<br />

q r r p p q<br />

A R <br />

A R<br />

1<br />

0 0<br />

<br />

Thus, the given result is proved.<br />

Question 23:<br />

If the first and the<br />

terms, prove that<br />

P<br />

th<br />

n term of a G.P. are a and b , respectively, and if P<br />

<br />

<br />

ab<br />

<br />

2 n<br />

Solution 23:<br />

The first term of the G.P is a<br />

Therefore, the G.P. is<br />

<br />

n<br />

b ar 1<br />

....... 1<br />

P Product of n<br />

<br />

terms<br />

2 n 1<br />

aarar ......<br />

ar <br />

<br />

2 n 1<br />

a a .... ar r .... r <br />

<br />

<br />

<br />

<br />

<br />

n 1 2 .... n<br />

a r 1<br />

....... 2<br />

Here,<br />

<br />

1,2,..... n 1<br />

1 2 ....... n 1<br />

<br />

<br />

.<br />

and the last term is b .<br />

a, ar, ar , ar .... ar <br />

is an A.P.<br />

<br />

2 3 n 1<br />

, where r<br />

n1 n1<br />

n n1<br />

2 n<br />

1 1 1 2 n 2<br />

2<br />

<br />

<br />

2 2<br />

P <br />

<br />

<br />

nn1<br />

n 2<br />

a r<br />

P a r<br />

2 2n<br />

nn1<br />

<br />

<br />

n<br />

2 n 1<br />

a r <br />

1 n<br />

<br />

<br />

<br />

<br />

is the common ratio.<br />

is the product of n<br />

<br />

<br />

n<br />

aar <br />

<br />

<br />

n<br />

ab Using 1<br />

<br />

<br />

Thus, the given result is proved.<br />

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