Q. 6 B

# Find the interval

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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