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Grade: 12

I have got the answer of the question which satisfies the condition given, but its not actually the answer, the question is:-

log(ax) - 2log(x+1) = 0 . What is the value of a for which the above equation has exactly 1 root?

The answer which I got is 4. It satisfies the quadratic as well as log. But the teacher cut the whole marks. I dont know the answer, since it was the test paper of my friend and he had got no marks for getting 4. The question is of 8 marks, so it shouldnt be that easy. Please help me.

10 years ago

Answers : (1)

Badiuddin askIITians.ismu Expert
147 Points

Dear avijit


log(ax) - 2log(x+1) = 0

for this

ax>0   and x+1>0


lets solve

 log(ax) - 2log(x+1) = 0

or ax= (x+1)2

or x2 + x(2-a) +1=0

for unique solution discrimnent must be zero

 which give a=0 or 4

but ax>0 so a can't be zero

for a=4   x=1 is solution

which satisfy the given equation

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10 years ago
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