JEE AdvancedMathematicsApplication of DerivativesNumerical+4 / −1
Let be a function defined on (the set of all real numbers) such that for all If is a function defined on with values in the interval such that then the number of points in at which has a local maximum is .
Numerical answer
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Correct answer: 1
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We are given Also, with for all .
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Since and is a strictly increasing function on , the local maxima/minima of and occur at the same points.
Indeed, Since , and always have the same sign. Hence the intervals of increase/decrease of and are identical.
So it is enough to count the number of local maxima of .
- Critical points come from : Now analyze sign changes of .
Because the constant , the sign depends on
Notice:
- is always nonnegative and has even multiplicity, so it does not change sign across .
- is always nonnegative and has even multiplicity, so it does not change sign across .
- changes sign across .
- changes sign across .
Thus the sign of is essentially the sign of
- Check intervals:
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For :
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For :
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For : again
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For :
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For :
So the sign chart is: no sign change at , no sign change at .
- Therefore:
- At , changes from increasing to decreasing, so has a local maximum.
- At , has a local minimum.
- At and , there is no local extremum.
Hence also has exactly one local maximum.
- Final answer:
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