NCERT Class XI Mathematics - Sequences and Series - Solutions

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Question : 62
Total: 106
The sum of two numbers is 6 times their geometric mean, show that numbers are in the ratio (3+22):(322).
Solution:  
Let a and b be the two numbers such that a + b = 6 ab
⇒ a + b = 3 (2ab) ⇒
a+b
2ab
=
3
1

Applying componendo and dividendo, we have,
a+b+2ab
a+b2ab
=
3+1
31

(a+b)2
(ab)2
=
4
2
a+b
ab
=
2
1

Again applying componendo & dividendo, we have
(a+b)+(ab)
(a+b)(ab)
=
2+1
21
2a
2b
=
2+1
21
a
b
=
2+1
21

Squaring both sides, we get
a
b
=
(2+1)2
(21)2
=
2+1+22
2+122
a
b
=
3+22
322

Hence, proved.
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