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F(X) = X3 − 3x . - CBSE (Science) Class 12 - Mathematics

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Question

f(x) = x\[-\] 3x .

Solution

\[\text { Given: } \hspace{0.167em} f\left( x \right) = \left( x - 5 \right)^4 \]

\[ \Rightarrow f'\left( x \right) = 4 \left( x - 5 \right)^3 \]

\[\text { For a local maximum or a local minimum, we must have }\]

\[f'\left( x \right) = 0\]

\[ \Rightarrow 4 \left( x - 5 \right)^3 = 0\]

\[ \Rightarrow x = 5\]

Since f '(x) changes from negative to positive as x increases through 1, x = 1 is the point of local minima.
The local minimum value of  f (x) at x = 1 is given by \[\left( 1 \right)^3 - 3\left( 1 \right) = - 2\]

Since f '(x) changes from positive to negative when x increases through -1, x = -1 is the point of local maxima.
The local maximum value of  f (x) at x = -1 is given by \[\left( - 1 \right)^3 - 3\left( - 1 \right) = 2\]

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Solution F(X) = X3 − 3x . Concept: Graph of Maxima and Minima.
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