Question:

Prove that the function given by f(x)=x3-3x2+3x-100 is increasing in R

Updated On: Oct 11, 2023
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Solution and Explanation

We have,

f(x)=x3-3x2+3x-100

f'(x)=3x2-6x+3

=3(x2-2x+1)

=3(x-1)2

For any x∈R, (x − 1)2 > 0.

Thus, f'(x) is always positive in R.

Hence, the given function (f) is increasing in R

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Concepts Used:

Increasing and Decreasing Functions

Increasing Function:

On an interval I, a function f(x) is said to be increasing, if for any two numbers x and y in I such that x < y, 

⇒ f(x) ≤ f(y)

Decreasing Function:

On an interval I, a function f(x) is said to be decreasing, if for any two numbers x and y in I such that x < y,

⇒ f(x) ≥ f(y)

Strictly Increasing Function:

On an interval I, a function f(x) is said to be strictly increasing, if for any two numbers x and y in I such that x < y,

⇒ f(x) < f(y)

Strictly Decreasing Function:

On an interval I, a function f(x) is said to be strictly decreasing, if for any two numbers x and y in I such that x < y,

⇒ f(x) > f(y)

Graphical Representation of Increasing and Decreasing Functions