Thanks, that was pretty simple

Find two quadratic functions f and g such that and and both have a maximum value of 18.

So if then for both f and g.

I also got for both f and g

what do I do from here?

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- January 15th 2011, 08:29 PMjgv115Quadratic problem
Thanks, that was pretty simple

Find two quadratic functions f and g such that and and both have a maximum value of 18.

So if then for both f and g.

I also got for both f and g

what do I do from here? - January 15th 2011, 09:10 PMabhishekkgp
the question basically is that how many quadratic functions are there satisfying

and the maximum value attained by f is 18.

since 1 is a root of , we can write

; p being the other root.

given that , we have .

also maximum value of is 18 and we know that the maxima occurs at as p and 1 are the roots of f, we have

, which simplifies to,

. now multiply both sides by k to get,

. we already have the value of which is 10, so we have,

which gives two values of k which are . both are acceptable as k had to be negative( if k is not negative then maxima of f does not exist).

corresponding values of p are -5 and -0.2.

so we have two such quadratic functions which can be found out by putting the values of k and p in - January 15th 2011, 09:21 PMabhishekkgp
to proceed from here you have to exploit on the information that maxima of is 18.

you must already be aware that the maxima(or minima) occurs at where and are the roots of the quadratic equation.

now you must also be knowing that sum of roots can be expressed in terms of the coefficients of powers of x, viz, .

so you will get that maximum of f occurs at .

so use . from this you will get one more relation in a and b. knowing that your problem can be solved.