Q. 6 B 3.6( 16 Votes )

Find the intervals in which the following functions are strictly increasing or decreasing:

10 – 6x – 2x2

Answer :

It is given that function f(x) = 10 – 6x – 2x2


f’(x) = -6 – 4x


If f’(x) = 0, then we get,


x =


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



So, in interval

x < -3/2
-4x > 6
-6 - 4x > 0

f’(x) = -6 – 4x > 0

Therefore, the given function (f) is strictly increasing in interval.


And in interval 

f’(x) = -6 – 4x < 0

Therefore, the given function (f) is strictly decreasing in interval .


Thus, f is strictly decreasing for x > .

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