sequence series 1


If a1,a2,a3..............an are n postive numbers in arithmetic progression with common difference d≠0 and Sn = a1 + a2 + ... + an

a. Sn __ n - 2(√a1 + √a2 +...+√an) (>,<,=,≤,≥ or cannot say)

b. 2Sn2 > (np . a1 . an)
Find maximum value of p.

6 Answers

39
Dr.House ·

good one.
1st one is > .
i am at present not able to find if any equality will occur.

1
dimensions (dimentime) ·


by AM GM ineq.

1+a1≥2√a1

1+a2≥2√a2
.
.
.

1+an≥2√an

adding all

Sn≥-(n-2(√a1+√a2+...+√an))
so,

it will always be greater than RHS

second part is not clearly visible,

11
rkrish ·

@ dimensions....
your approach was correct (but there was a mistake in the conclusion)...

Using AM-GM,

1 + a1 > 2√a1
1 + a2 > 2√a2
.
.
.
1 + an > 2√an

Adding,

n + Sn > 2( √a1 + √a2 +...+ √an ) (Equality is not permissible bec. all ai's cannot be equal to 1 simultaneously as 'd≠0')

\Rightarrow Sn > 2( √a1 + √a2 +...+ √an ) - n

\Rightarrow Sn > - (n - 2( √a1 + √a2 +...+ √an ))

BUT Sn < or > n - 2( √a1 + √a2 +...+ √an ) cannot be said !!!!!

11
Subash ·

what about the second one rkrish?

is my answer rite?

11
rkrish ·

@ Subash...

question is not 2Sn2 > np . √a1an

It is 2Sn2 > np . a1 . an

11
Subash ·

k ill delete the above one

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