Answer :

It is given that function f(x) = 6 – 9x – x2


f’(x) = -9 – 2x


If f’(x) = 0, then we get,


x =


So, the point x = divides the real line into two disjoint intervals,



So, in interval


f’(x) = -9 – 2x > 0


Therefore, the given function (f) is strictly increasing for x < .


And in interval


f’(x) = -9 – 2x < 0


Therefore, the given function (f) is strictly decreasing for x>.


Thus, f is strictly decreasing for x>.


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