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Question

If the equations x2+b2=12bx and x2+a2=12ax have one and only one common root, then the value of |ab| is

A
1
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B
0
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C
2
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D
None of these
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Solution

The correct option is C 2
Here ab,
For a=b two equations become identical, so they have two roots in common.
Let α be the common root of the given equations. Then,
α2+b2=12bα(1)α2+a2=12aα(2)
Using equation (1) and (2),
b2a2=2(ab)αα=(a+b)2
Putting the value in equation (1),
(a+b)24+b2=1+2b×a+b2(a+b)2+4b2=4+4b2+4ab(a+b)24ab=4(ab)2=4|ab|=2

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