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Provide solution for RD Sharma maths class 12 chapter Increasing and Decreasing Functions exercise 16.2 question 22

Answers (1)

Answer:

f(x) is an increasing on the interval [4, 6].

Given:

f(x)=x^{2}-6x+3

To prove:

We have to prove that f(x) is an increasing on the interval [4, 6].

Hint:

A function f(x) is said to be increasing on [a, b] if f’(x) > 0.

Solution:

Given

f(x)=x^{2}-6x+3

On differentiating both sides w.r.t x we get

\begin{aligned} &\Rightarrow f^{\prime}(x)=\frac{d}{d x}\left(x^{2}-6 x+38\right) \\ &\Rightarrow f^{\prime}(x)=2 x-6 \\ &\Rightarrow f^{\prime}(x)=2(x-3) \\ \end{aligned}

\begin{aligned} &\text { Again, } x \in[4,6] \\ &\Rightarrow 4 \leq x \leq 6 \\ &\Rightarrow 1 \leq x-3 \leq 3 \\ &\Rightarrow(x-3)>0 \\ &\Rightarrow 2(x-3)>0 \\ &\Rightarrow f^{\prime}(x)>0 \end{aligned}

Thus f(x) is an increasing function x \in [4, 6]

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Gurleen Kaur

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