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Let f(x) = 8x^3 - 3x^2Then f(x) has a relative minimum atx=

Let f(x) = 8x^3 - 3x^2Then f(x) has a relative minimum atx=-example-1
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\begin{gathered} \mathrm{Minimum}((1)/(4),\: -(1)/(16)) \\ \mathrm{Maximum}(0,\: 0) \\ Inflection\: Point\colon((1)/(8),-(1)/(32)) \end{gathered}

1) To find the relative maxima of a function, we need to perform the first derivative test. It tells us whether the function has a local maximum, minimum r neither.


\begin{gathered} f^(\prime)(x)=(d)/(dx)\mleft(8x^3-3x^2\mright) \\ f^(\prime)(x)=(d)/(dx)\mleft(8x^3\mright)-(d)/(dx)\mleft(3x^2\mright) \\ f^(\prime)(x)=24x^2-6x \end{gathered}

2) Let's find the points equating the first derivative to zero and solving it for x:


\begin{gathered} 24x^2-6x=0 \\ x_{}=(-\left(-6\right)\pm\:6)/(2\cdot\:24),\Rightarrow x_1=(1)/(4),x_2=0 \\ f^(\prime)(x)>0 \\ 24x^2-6x>0 \\ (24x^2)/(6)-(6x)/(6)>(0)/(6) \\ 4x^2-x>0 \\ x\mleft(4x-1\mright)>0 \\ x<0\quad \mathrm{or}\quad \: x>(1)/(4) \\ f^(\prime)(x)<0 \\ 24x^2-6x<0 \\ 4x^2-x<0 \\ x\mleft(4x-1\mright)<0 \\ 0Now, we can write out the intervals, and combine them with the domain of this function since it is a polynomial one that has no discontinuities:[tex]\mathrm{Increasing}\colon-\infty\: <strong>3) </strong> Finally, we need to plug the x-values we've just found into the original function to get their corresponding y-values:[tex]\begin{gathered} f(x)=8x^3-3x^2 \\ f(0)=8(0)^3-3(0)^2 \\ f(0)=0 \\ \mathrm{Maximum}\mleft(0,0\mright) \\ x=(1)/(4) \\ f((1)/(4))=8\mleft((1)/(4)\mright)^3-3\mleft((1)/(4)\mright)^2 \\ \mathrm{Minimum}\mleft((1)/(4),-(1)/(16)\mright) \end{gathered}

4) Finally, for the inflection points. We need to perform the 2nd derivative test:


\begin{gathered} f^(\doubleprime)(x)=(d^2)/(dx^2)\mleft(8x^3-3x^2\mright) \\ f\: ^(\prime\prime)\mleft(x\mright)=(d)/(dx)\mleft(24x^2-6x\mright) \\ f\: ^(\prime\prime)(x)=48x-6 \\ 48x-6=0 \\ 48x=6 \\ x=(6)/(48)=(1)/(8) \end{gathered}

Now, let's plug this x value into the original function to get the y-corresponding value:


\begin{gathered} f(x)=8x^3-3x^2 \\ f((1)/(8))=8((1)/(8))^3-3((1)/(8))^2 \\ f((1)/(8))=-(1)/(32) \\ Inflection\: Point\colon((1)/(8),-(1)/(32)) \end{gathered}