# 3.6 Zeros of polynomial functions  (Page 8/14)

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$f\left(x\right)=2{x}^{3}+3{x}^{2}+x+6;\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}x+2$

$-2$

$f\left(x\right)=-5{x}^{3}+16{x}^{2}-9;\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}x-3$

${x}^{3}+3{x}^{2}+4x+12;\text{\hspace{0.17em}}x+3$

$-3$

$4{x}^{3}-7x+3;\text{\hspace{0.17em}}x-1$

$2{x}^{3}+5{x}^{2}-12x-30,\text{​}\text{\hspace{0.17em}}2x+5$

For the following exercises, use the Rational Zero Theorem to find all real zeros.

${x}^{3}-3{x}^{2}-10x+24=0$

$2{x}^{3}+7{x}^{2}-10x-24=0$

${x}^{3}+2{x}^{2}-9x-18=0$

${x}^{3}+5{x}^{2}-16x-80=0$

${x}^{3}-3{x}^{2}-25x+75=0$

$2{x}^{3}-3{x}^{2}-32x-15=0$

$2{x}^{3}+{x}^{2}-7x-6=0$

$2{x}^{3}-3{x}^{2}-x+1=0$

$3{x}^{3}-{x}^{2}-11x-6=0$

$2{x}^{3}-5{x}^{2}+9x-9=0$

$\frac{3}{2}$

$2{x}^{3}-3{x}^{2}+4x+3=0$

${x}^{4}-2{x}^{3}-7{x}^{2}+8x+12=0$

${x}^{4}+2{x}^{3}-9{x}^{2}-2x+8=0$

$4{x}^{4}+4{x}^{3}-25{x}^{2}-x+6=0$

$2{x}^{4}-3{x}^{3}-15{x}^{2}+32x-12=0$

${x}^{4}+2{x}^{3}-4{x}^{2}-10x-5=0$

$4{x}^{3}-3x+1=0$

$8{x}^{{}^{4}}+26{x}^{3}+39{x}^{2}+26x+6$

For the following exercises, find all complex solutions (real and non-real).

${x}^{3}+{x}^{2}+x+1=0$

${x}^{3}-8{x}^{2}+25x-26=0$

${x}^{3}+13{x}^{2}+57x+85=0$

$3{x}^{3}-4{x}^{2}+11x+10=0$

${x}^{4}+2{x}^{3}+22{x}^{2}+50x-75=0$

$2{x}^{3}-3{x}^{2}+32x+17=0$

## Graphical

For the following exercises, use Descartes’ Rule to determine the possible number of positive and negative solutions. Confirm with the given graph.

$f\left(x\right)={x}^{3}-1$

$f\left(x\right)={x}^{4}-{x}^{2}-1$

1 positive, 1 negative

$f\left(x\right)={x}^{3}-2{x}^{2}-5x+6$

$f\left(x\right)={x}^{3}-2{x}^{2}+x-1$

3 or 1 positive, 0 negative

$f\left(x\right)={x}^{4}+2{x}^{3}-12{x}^{2}+14x-5$

$f\left(x\right)=2{x}^{3}+37{x}^{2}+200x+300$

0 positive, 3 or 1 negative

$f\left(x\right)={x}^{3}-2{x}^{2}-16x+32$

$f\left(x\right)=2{x}^{4}-5{x}^{3}-5{x}^{2}+5x+3$

2 or 0 positive, 2 or 0 negative

$f\left(x\right)=2{x}^{4}-5{x}^{3}-14{x}^{2}+20x+8$

$f\left(x\right)=10{x}^{4}-21{x}^{2}+11$

2 or 0 positive, 2 or 0 negative

## Numeric

For the following exercises, list all possible rational zeros for the functions.

$f\left(x\right)={x}^{4}+3{x}^{3}-4x+4$

$f\left(x\right)=2{x}^{{}^{3}}+3{x}^{2}-8x+5$

$f\left(x\right)=3{x}^{{}^{3}}+5{x}^{2}-5x+4$

$f\left(x\right)=6{x}^{4}-10{x}^{2}+13x+1$

$f\left(x\right)=4{x}^{5}-10{x}^{4}+8{x}^{3}+{x}^{2}-8$

## Technology

For the following exercises, use your calculator to graph the polynomial function. Based on the graph, find the rational zeros. All real solutions are rational.

$f\left(x\right)=6{x}^{3}-7{x}^{2}+1$

$f\left(x\right)=4{x}^{3}-4{x}^{2}-13x-5$

$f\left(x\right)=8{x}^{3}-6{x}^{2}-23x+6$

$f\left(x\right)=12{x}^{4}+55{x}^{3}+12{x}^{2}-117x+54$

$f\left(x\right)=16{x}^{4}-24{x}^{3}+{x}^{2}-15x+25$

$\frac{5}{4}$

## Extensions

For the following exercises, construct a polynomial function of least degree possible using the given information.

Real roots: –1, 1, 3 and $\text{\hspace{0.17em}}\left(2,f\left(2\right)\right)=\left(2,4\right)$

Real roots: –1 (with multiplicity 2 and 1) and $\text{\hspace{0.17em}}\left(2,f\left(2\right)\right)=\left(2,4\right)$

$f\left(x\right)=\frac{4}{9}\left({x}^{3}+{x}^{2}-x-1\right)$

Real roots: –2, $\text{\hspace{0.17em}}\frac{1}{2}\text{\hspace{0.17em}}$ (with multiplicity 2) and $\text{\hspace{0.17em}}\left(-3,f\left(-3\right)\right)=\left(-3,5\right)$

Real roots: $\text{\hspace{0.17em}}-\frac{1}{2}\text{\hspace{0.17em}}$ , 0, $\text{\hspace{0.17em}}\frac{1}{2}\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}\left(-2,f\left(-2\right)\right)=\left(-2,6\right)$

$f\left(x\right)=-\frac{1}{5}\left(4{x}^{3}-x\right)$

Real roots: –4, –1, 1, 4 and $\text{\hspace{0.17em}}\left(-2,f\left(-2\right)\right)=\left(-2,10\right)$

## Real-world applications

For the following exercises, find the dimensions of the box described.

The length is twice as long as the width. The height is 2 inches greater than the width. The volume is 192 cubic inches.

8 by 4 by 6 inches

The length, width, and height are consecutive whole numbers. The volume is 120 cubic inches.

The length is one inch more than the width, which is one inch more than the height. The volume is 86.625 cubic inches.

5.5 by 4.5 by 3.5 inches

The length is three times the height and the height is one inch less than the width. The volume is 108 cubic inches.

The length is 3 inches more than the width. The width is 2 inches more than the height. The volume is 120 cubic inches.

8 by 5 by 3 inches

For the following exercises, find the dimensions of the right circular cylinder described.

The radius is 3 inches more than the height. The volume is $\text{\hspace{0.17em}}16\pi \text{\hspace{0.17em}}$ cubic meters.

The height is one less than one half the radius. The volume is $\text{\hspace{0.17em}}72\pi \text{\hspace{0.17em}}$ cubic meters.

Radius = 6 meters, Height = 2 meters

The radius and height differ by one meter. The radius is larger and the volume is $\text{\hspace{0.17em}}48\pi \text{\hspace{0.17em}}$ cubic meters.

The radius and height differ by two meters. The height is greater and the volume is $\text{\hspace{0.17em}}28.125\pi \text{\hspace{0.17em}}$ cubic meters.

Radius = 2.5 meters, Height = 4.5 meters

80. The radius is $\text{\hspace{0.17em}}\frac{1}{3}\text{\hspace{0.17em}}$ meter greater than the height. The volume is $\text{\hspace{0.17em}}\frac{98}{9}\pi \text{\hspace{0.17em}}$ cubic meters.

The average annual population increase of a pack of wolves is 25.
how do you find the period of a sine graph
Period =2π if there is a coefficient (b), just divide the coefficient by 2π to get the new period
Am
if not then how would I find it from a graph
Imani
by looking at the graph, find the distance between two consecutive maximum points (the highest points of the wave). so if the top of one wave is at point A (1,2) and the next top of the wave is at point B (6,2), then the period is 5, the difference of the x-coordinates.
Am
you could also do it with two consecutive minimum points or x-intercepts
Am
I will try that thank u
Imani
Case of Equilateral Hyperbola
ok
Zander
ok
Shella
f(x)=4x+2, find f(3)
Benetta
f(3)=4(3)+2 f(3)=14
lamoussa
14
Vedant
pre calc teacher: "Plug in Plug in...smell's good" f(x)=14
Devante
8x=40
Chris
Explain why log a x is not defined for a < 0
the sum of any two linear polynomial is what
Momo
how can are find the domain and range of a relations
the range is twice of the natural number which is the domain
Morolake
A cell phone company offers two plans for minutes. Plan A: $15 per month and$2 for every 300 texts. Plan B: $25 per month and$0.50 for every 100 texts. How many texts would you need to send per month for plan B to save you money?
6000
Robert
more than 6000
Robert
can I see the picture
How would you find if a radical function is one to one?
how to understand calculus?
with doing calculus
SLIMANE
Thanks po.
Jenica
Hey I am new to precalculus, and wanted clarification please on what sine is as I am floored by the terms in this app? I don't mean to sound stupid but I have only completed up to college algebra.
I don't know if you are looking for a deeper answer or not, but the sine of an angle in a right triangle is the length of the opposite side to the angle in question divided by the length of the hypotenuse of said triangle.
Marco
can you give me sir tips to quickly understand precalculus. Im new too in that topic. Thanks
Jenica
if you remember sine, cosine, and tangent from geometry, all the relationships are the same but they use x y and r instead (x is adjacent, y is opposite, and r is hypotenuse).
Natalie
it is better to use unit circle than triangle .triangle is only used for acute angles but you can begin with. Download any application named"unit circle" you find in it all you need. unit circle is a circle centred at origine (0;0) with radius r= 1.
SLIMANE
What is domain
johnphilip
the standard equation of the ellipse that has vertices (0,-4)&(0,4) and foci (0, -15)&(0,15) it's standard equation is x^2 + y^2/16 =1 tell my why is it only x^2? why is there no a^2?
what is foci?
This term is plural for a focus, it is used for conic sections. For more detail or other math questions. I recommend researching on "Khan academy" or watching "The Organic Chemistry Tutor" YouTube channel.
Chris
how to determine the vertex,focus,directrix and axis of symmetry of the parabola by equations