JEE 2009 ..analytical

let S1, S2......... be the squares such that for each n≥1, the length of a side of Sn equals the length of a diagonal of sn+1. if the length of a side of S1 is 10cm, then for which of the following values of n is the area of Sn less than 1sq.cm ?

a) 7

b) 8

c) 9

d) 10

9 Answers

1
skygirl ·

if i remember it correctly...

the ans is n>7

so n =8,9,10.

1
kshatriyan c ·

ha lekin kaise ??

62
Lokesh Verma ·

Arrey I gave this question just 2 days back.. this is a jee past question..

yes the answer is 8

asis has replied just a couple of days back..

1
kshatriyan c ·

sir whats the topic header ??

link ?

1
kshatriyan c ·

not just 8 bhaiya ...8 onwards

11
Anirudh Narayanan ·

the sides of the squares form an decreasing gp..... a=10 and r=1/√2

if an is side of nth square,

Area= (an)2

thus the area will form a decreasing gp of their own with a=100 and r= 1/2....

An<1

a.rn-1<1

(1/2)n-1<1/100

2n-1>100

But 26 is less than 100 => n-1 > 6 ==> n>7

PLS DON'T PINK ME....I FOUND OUT THE MISTAKE AND THEN CHANGED THE ANSWER....

11
Anirudh Narayanan ·

pls find the mistake....bhaiya

1
skygirl ·

1
Kalyan Pilla ·

The answer is 8,9,10

side of nth square an=10/(√2)n-1

Area of nth square = 100/2n-1

Therefore n=8

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