Calculus 1 : How to graph functions of points

Study concepts, example questions & explanations for Calculus 1

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Example Questions

Example Question #1 : Other Points

Find the critical points (rounded to two decimal places):

 \displaystyle f(x)= x^3+3x^2+x

Possible Answers:

\displaystyle c=0.18\ and\ c=1.82

\displaystyle c=-0.25\ and\ c=-2.41

\displaystyle c=-0.18\ and\ c=-1.82

\displaystyle c=0.25\ and\ c=2.41

Correct answer:

\displaystyle c=-0.18\ and\ c=-1.82

Explanation:

To find the critical points, set \displaystyle f{}'(x)=0 and solve for \displaystyle x.

\displaystyle f(x)= x^3+3x^2+x

Differentiate:

\displaystyle f{}'(x)= 3x^2+6x+1

Set equal to zero:

\displaystyle 3x^2+6x+1=0

Solve for \displaystyle x using the quadratic formula: \displaystyle x= \frac{-b\pm \sqrt{b^2-4ac}}{2a}

\displaystyle a=3,\ b=6,\ c=1

\displaystyle x= \frac{-6\pm \sqrt{(6)^2-4(3)(1)}}{2(3)}

\displaystyle c=-0.18\ and\ c=-1.82

Example Question #2 : How To Graph Functions Of Points

Find the \displaystyle x value(s) of the critical point(s) of

\displaystyle f(x)=x^3+2x^2+x+4.

Possible Answers:

\displaystyle \\ c_1=\frac{1}{3} \\ \\ c_2=1

\displaystyle \\ c_1=-\frac{1}{3} \\ \\ c_2=-1

There are no real answers.

\displaystyle \\ c_1=3 \\ \\ c_2=-1

\displaystyle \\ c_1=-3 \\ \\ c_2=1

Correct answer:

\displaystyle \\ c_1=-\frac{1}{3} \\ \\ c_2=-1

Explanation:

In order to find the critical points, we must find \displaystyle \ f'(x) and solve for \displaystyle \ x

\displaystyle f(x)=x^3+2x^2+x+4

\displaystyle \\ \\ f'(x)=3x^2+4x+1

Set  \displaystyle f'(x)=0

\displaystyle \\ \\ 3x^2+4x+1=0

Use the quadratic equation to solve for \displaystyle \ x.

Remember that the quadratic equation is as follows.

 

\displaystyle \\ \\ x=\frac{-b\pm\sqrt{b^2-4\cdot a\cdot c}}{2\cdot a}, where a,b and c refer to the coefficents in the

equation  \displaystyle ax^2+bx+c=0.

In this case, \displaystyle a=3, \displaystyle b=4, and \displaystyle c=1.

After plugging in those values, we get

\displaystyle \\ \\ x=\frac{-4\pm\sqrt{4^2-4\cdot3\cdot1}}{2\cdot3} =\frac{-4 \pm \sqrt{4}}{6}=\frac{-4 \pm 2}{6}.

So the critical points \displaystyle x values are:

\displaystyle \\ \\ c_1=\frac{-4+2}{6}=\frac{-1}{3}

\displaystyle \\ \\ c_2=\frac{-4-2}{6}=-1

Example Question #3 : How To Graph Functions Of Points

Find the \displaystyle x value(s) of the critical point(s) of

\displaystyle f(x)=5x^3+10x^2+x+100.

Possible Answers:

\displaystyle \\ c_1=0 \\ \\ c_2=0

\displaystyle \\ c_1=\frac{-10+\sqrt{85}}{15} \\ \\ c_2=\frac{-10-\sqrt{85}}{15}

\displaystyle \\ c_1=\frac{\sqrt{85}}{15} \\ \\ c_2=\frac{-\sqrt{85}}{15}

\displaystyle \\ c_1=1 \\ \\ c_2=0

\displaystyle \\ c_1=\frac{-10+\sqrt{85}}{30} \\ \\ c_2=\frac{-10-\sqrt{85}}{30}

Correct answer:

\displaystyle \\ c_1=\frac{-10+\sqrt{85}}{15} \\ \\ c_2=\frac{-10-\sqrt{85}}{15}

Explanation:

In order to find the critical points, we must find \displaystyle \ f'(x) and solve for \displaystyle \ x.

\displaystyle \\ \\ f(x)=5x^3+10x^2+x+100

\displaystyle \\ \\ f'(x)=15x^2+20x+1

Set  \displaystyle \ f'(x)=0 

\displaystyle \\ \\ 15x^2+20x+1=0

Use the quadratic equation to solve for \displaystyle \ x.

Remember that the quadratic equation is as follows.

 \displaystyle \\ \\ x=\frac{-b\pm\sqrt{b^2-4\cdot a\cdot c}}{2\cdot a}, where a,b and c refer to the coefficents in the equation  \displaystyle ax^2+bx+c=0.

 

In this case, \displaystyle a=15, \displaystyle b=20, and \displaystyle c=1.

After plugging in those values, we get. 

 

\displaystyle {}\\ x=\frac{-20\pm\sqrt{20^2-4\cdot15\cdot1}}{2\cdot15} =\frac{-20 \pm \sqrt{340}}{30} \\ \\ x=\frac{-20 \pm 2\cdot\sqrt{85}}{30} 

So the critical points \displaystyle x values are,

\displaystyle {}\\ \\ c_1=\frac{-20+2\cdot \sqrt{85}}{30}=\frac{-10+\sqrt{85}}{15} \\ \\ c_2=\frac{-20-2\cdot \sqrt{85}}{30}=\frac{-10-\sqrt{85}}{15}

Example Question #101 : Graphing Functions

Find the critical points of

\displaystyle f(x)=x^3+3x^2+x+5

Possible Answers:

The critical points are complex.

\displaystyle \\ c_1=0\\\\\ c_2=-1-\frac{\sqrt{6}}{3}

 

\displaystyle \\ c_1=\frac{\sqrt{6}}{3}\\\\\ c_2=-\frac{\sqrt{6}}{3}

\displaystyle \\ c_1=-1+\frac{\sqrt{6}}{3}\\\\\ c_2=-1-\frac{\sqrt{6}}{3}

Correct answer:

\displaystyle \\ c_1=-1+\frac{\sqrt{6}}{3}\\\\\ c_2=-1-\frac{\sqrt{6}}{3}

Explanation:

First we need to find \displaystyle f'(x).

\displaystyle f(x)=x^3+3x^2+x+5

\displaystyle f'(x)=3x^2+6x+1

Now we set \displaystyle f'(x)=0.

\displaystyle 3x^2+6x+4=0.

 

Now we can use the quadratic equation in order to find the critical points.

Remember that the quadratic equation is 

\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a},

where a,b,c refer to the coefficients in the equation

\displaystyle ax^2+bx+c=0

 

In this case, a=3, b=6, and c=1. 

\displaystyle x=\frac{-6\pm\sqrt{(-6)^2-4(3)(1)}}{(2)(3)}

 

\displaystyle x=\frac{-6\pm\sqrt{24}}{6}=\frac{-6\pm2\sqrt{6}}{6}

 

Thus are critical points are

\displaystyle c_1=\frac{-6+2\sqrt{6}}{6}=-1+\frac{\sqrt{6}}{3}

\displaystyle c_2=\frac{-6-2\sqrt{6}}{6}=-1-\frac{\sqrt{6}}{3}

 

Example Question #5 : Other Points

Find the critical points of

\displaystyle f(x)=x^2-2x+1.

Possible Answers:

There are no critical points.

\displaystyle x=2

\displaystyle x=1

\displaystyle x=0

Correct answer:

\displaystyle x=1

Explanation:

In order to find the critical points, we need to find \displaystyle f'(x) using the power rule \displaystyle f(x)=x^n \rightarrow f'(x)=nx^{n-1}.

\displaystyle f(x)=x^2-2x+1

\displaystyle f'(x)=2x-2

Now we set \displaystyle f'(x)=0, and solve for \displaystyle x.

\displaystyle 2x-2=0

\displaystyle 2x=2

\displaystyle x=1

Thus \displaystyle x=1 is a critical point.

Example Question #1 : How To Graph Functions Of Points

Find the critical point(s) of \displaystyle f(x)=2x^{2}-5x+4.

Possible Answers:

\displaystyle c=\frac{5}{4}

\displaystyle c=\frac{4}{5} 

\displaystyle c=\frac{5}{4} and \displaystyle c=-\frac{5}{4}

\displaystyle c=\frac{4}{5} and \displaystyle c=-\frac{4}{5}

\displaystyle c=\frac{5}{4} and \displaystyle c=-\frac{4}{5}

Correct answer:

\displaystyle c=\frac{5}{4}

Explanation:

To find the critical point(s) of a function \displaystyle f(x), take its derivative \displaystyle f'(x), set it equal to \displaystyle 0, and solve for \displaystyle x.

Given \displaystyle f(x)=2x^{2}-5x+4, use the power rule

\displaystyle f(x)=x^n \rightarrow f'(x)=nx^{n-1} to find the derivative. Thus the derivative is, \displaystyle f'(x)=4x-5=0.

Since \displaystyle 4x-5=0:

\displaystyle 4x=5

\displaystyle x=\frac{5}{4}

The critical point \displaystyle c is \displaystyle c=\frac{5}{4}

Example Question #101 : Graphing Functions

Find the critical points of

\displaystyle f(x)=3x^3-20x^2+4x+99.

Possible Answers:

\displaystyle c=\frac{20-2\sqrt{91}}{9}

There are no critical points

\displaystyle \\ c_1=\frac{20+2\sqrt{91}}{9} \\ \\ c_2=\frac{20-2\sqrt{91}}{9}

\displaystyle x=0

\displaystyle \\ c=\frac{20+2\sqrt{91}}{9}

Correct answer:

\displaystyle \\ c_1=\frac{20+2\sqrt{91}}{9} \\ \\ c_2=\frac{20-2\sqrt{91}}{9}

Explanation:

In order to find the critical points, we must find \displaystyle f'(x) using the power rule \displaystyle f(x)=x^n \rightarrow f'(x)=nx^{n-1}.

\displaystyle f(x)=3x^3-20x^2+4x+99

\displaystyle f'(x)=9x^2-40x+4.

Now we set \displaystyle f'(x)=0.

\displaystyle 9x^2-40x+4=0

Now we use the quadratic equation in order to solve for \displaystyle x.

Remember that the quadratic equation is as follows.

\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a},

where a,b,c correspond to the coefficients in the equation 

\displaystyle ax^2+bx+c=0.

In this case, a=9, b=-40, c=4.

\displaystyle x=\frac{40\pm\sqrt{(-40)^2-4(9)(4)}}{2(9)}

 

\displaystyle x=\frac{40\pm\sqrt{1600-144}}{18}

 

\displaystyle x=\frac{40\pm\sqrt{1456}}{18}=\frac{40\pm4\sqrt{91}}{18}

Then are critical points are:

 

\displaystyle c_1=\frac{40+4\sqrt{91}}{18}=\frac{20+2\sqrt{91}}{9}

\displaystyle c_2=\frac{40-4\sqrt{91}}{18}=\frac{20-2\sqrt{91}}{9}

Example Question #2 : Other Points

Find all the critical points of

\displaystyle f(x)=x^3-2x+10.

Possible Answers:

\displaystyle x=0

There are no critical points.

\displaystyle \\ x=\sqrt{\frac{2}{3}} \\ \\ x=-\sqrt{\frac{2}{3}}

\displaystyle \\ x=\sqrt{\frac{2}{3}}

\displaystyle x=-\sqrt{\frac{2}{3}}

Correct answer:

\displaystyle \\ x=\sqrt{\frac{2}{3}} \\ \\ x=-\sqrt{\frac{2}{3}}

Explanation:

In order to find the critical points, we first need to find \displaystyle f'(x) using the power rule \displaystyle f(x)=x^n \rightarrow f'(x)=nx^{n-1}..

\displaystyle f(x)=x^3-2x+10

\displaystyle f'(x)=3x^2-2

Now we set \displaystyle f'(x)=0.

\displaystyle 3x^2-2=0

\displaystyle 3x^2=2

\displaystyle x^2=\frac{2}{3}

\displaystyle x=\pm\sqrt{\frac{2}{3}}

Thus the critical points are at

\displaystyle x=\sqrt{\frac{2}{3}}, and

\displaystyle x=-\sqrt{\frac{2}{3}}.

Example Question #2 : How To Graph Functions Of Points

Find the critical points of the following function:

\displaystyle y=\frac{x^6}{6}+\frac{3x^5}{5}-\frac{13x^4}{4}-5x^3

Possible Answers:

\displaystyle x=\left \{ {{-5, -1, 0, 3}} \right \}

\displaystyle x=\left \{ {-5, -1, 0, 3} \right \}

\displaystyle x=\left \{ {-3, 0, 1, 5} \right \}

\displaystyle x=\left \{ {0, 1.332, 6.013} \right \}

\displaystyle x=\left \{ {-6.013, -1.332, 0} \right \}

Correct answer:

\displaystyle x=\left \{ {{-5, -1, 0, 3}} \right \}

Explanation:

To find critical points the derivative of the function must be found. 

\displaystyle y=\frac{x^6}{6}+\frac{3x^5}{5}-\frac{13x^4}{4}-5x^3

\displaystyle y'=x^5+3x^4-13x^3-15x^3

 

Critical points occur where the derivative equals zero. 

\displaystyle 0=x^5+3x^4-13x^3-15x^3

\displaystyle 0=x^2(x+1)(x+5)(x-3)

\displaystyle x=\left \{ {{-5, -1, 0, 3}} \right \}

Example Question #102 : Graphing Functions

Determine the point on the graph that is not changing if \displaystyle f(x)=x^{2}-12x+32.

Possible Answers:

\displaystyle (0,0)

\displaystyle (6,-2)

\displaystyle (0,-4)

\displaystyle (3,-2)

\displaystyle (6,-4)

Correct answer:

\displaystyle (6,-4)

Explanation:

To find the point where the graph of \displaystyle f(x) is not changing, we must set the first derivative equal to zero and solve for \displaystyle x.

To evaluate this derivate, we need the following formulae:

\displaystyle \frac{d}{dx}(c)=0, \frac{d}{dx}(x)=1, \frac{d}{dx}cx=c

\displaystyle \frac{d}{dx}(x^{n}))=nx^{n-1}, \frac{d}{dx}(cx^{n})=ncx^{n-1}

\displaystyle f'(x)=2x^{2-1}-12x^{1-1}+0=2x-12

Now, setting the derivate equal to \displaystyle 0 to find where the graph is not changing:

\displaystyle 2x-12=0 ==> x=6

Now, to find the corresponding \displaystyle y value, we plug this \displaystyle x value back into \displaystyle f(x):

\displaystyle f(6)=6^{2}-12(6)+32=36-72+32=-4

Therefore, the point where \displaystyle f(x) is not changing is \displaystyle (6,-4)

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