for what value of 'k' does the function
y=x3 - 3(7 - k)x2 -3(9-k2)x + 2 , x>0
have a point of maximum
62no i think there is more to it..
it is given x>0
so u will have to take that the derivative has a +ve root!
1i know the method, i want answer. my answer is not matching with that given in the book
its from a.das
62i am getting (-3,29/7)
to be true.. din do with utmost sincerity .. just rushed to get the answer.. tell me if it is correct or wrong.
and then the right answer and ur answer.. so that we can work more :)
1actual answer (-∞,3) U (3,29/7)
my answer (-∞,3) U (3,7)
1first of all derivative:
3x^2-6(7-k)x-3(9-k^2). this equation must have 2(one +ve x for maxima and another +ve x for minima) +ve roots. then,
at x=0, -3(9-k^2)>0,implying k^2>9. also derivative of above equation 6x-6(7-k)=0 must have a +ve root.(at the pt. of minima of the parabola.) so, 7>k.
but, discriminant should be>0, then we get k<29/7