Algebra II : Polynomial Functions

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #2 : Graphing Polynomial Functions

Which of the following is a graph for the following equation:

\displaystyle x^8+x^7-x^4+10

Possible Answers:

Correct answer

Cannot be determined

Incorrect 2

Incorrect 1

Incorrect 3

Correct answer:

Correct answer

Explanation:

The way to figure out this problem is by understanding behavior of polynomials.

The sign that occurs before the \displaystyle x^8 is positive and therefore it is understood that the function will open upwards. the "8" on the function is an even number which means that the function is going to be u-shaped. The only answer choice that fits both these criteria is:

 Correct answer

Example Question #1 : How To Graph A Quadratic Function

Possible Answers:

\displaystyle 3) \displaystyle y = (x+3)^{2}

\displaystyle 2) \displaystyle y = (x-2)^{2}

None of the above

\displaystyle 1) \displaystyle y = x^{2}

\displaystyle 4) \displaystyle y = -(x-2)^{2} - 2

Correct answer:

\displaystyle 3) \displaystyle y = (x+3)^{2}

Explanation:

Starting with \displaystyle y = x^{2}

\displaystyle (x-2)^{2} moves the parabola \displaystyle x^{2} by \displaystyle 2 units to the right.

Similarly \displaystyle (x+3)^{2} moves the parabola by \displaystyle 3 units to the left.

Hence the correct answer is option \displaystyle 3.

Example Question #6 : Graphing Polynomial Functions

\displaystyle Find\ the\ end\ behavior\ for \ the\ function\ f(x)=-x^3+5x^2-2x+7

Possible Answers:

\displaystyle As\ x\rightarrow\ -\infty; f(x)\rightarrow\infty; As\ x\rightarrow\infty; f(x)\rightarrow\infty;

\displaystyle As\ x\rightarrow\ -\infty; f(x)\rightarrow-\infty; As\ x\rightarrow\infty; f(x)\rightarrow-\infty;

\displaystyle As\ x\rightarrow\ -\infty; f(x)\rightarrow\infty; As\ x\rightarrow\infty; f(x)\rightarrow-\infty;

\displaystyle As\ x\rightarrow\ -\infty; f(x)\rightarrow-\infty; As\ x\rightarrow\infty; f(x)\rightarrow\infty;

Correct answer:

\displaystyle As\ x\rightarrow\ -\infty; f(x)\rightarrow\infty; As\ x\rightarrow\infty; f(x)\rightarrow-\infty;

Explanation:

When we look at the function we see that the highest power of the function is a 3 which means it is an "odd degree" function. This means that the right and left side of the function will approach opposite directions. *Remember O for Odd and O for opposite. 

In this case we also have a negative sign associated with the highest power portion of the function - this means that the function is flipped. 

Both of these combine to make this an "odd negative" function. 

Odd negative functions always have the right side of the function approaching down and the left side approaching up. 

We represent this mathematically by saying that as x approaches negative infinity (left side), the function will approach positive infinity: 

\displaystyle As\ x\rightarrow\ -\infty; f(x)\rightarrow\infty;

...and as x approaches positive infinity (right side) the function will approach negative infinity:

\displaystyle As\ x\rightarrow\infty; f(x)\rightarrow-\infty;

 

Example Question #4 : Graphing Polynomial Functions

\displaystyle List\ the\ x-intercepts\ for\ the\ function\ below:

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

Possible Answers:

\displaystyle x=-1, x=2, x=\pm 5

\displaystyle x=1, x=-2, x=\pm 5

\displaystyle x=1, x=-2, x=5

\displaystyle x=-1, x=2, x=-5

Correct answer:

\displaystyle x=1, x=-2, x=5

Explanation:

\displaystyle To\ find\ the\ x-intercepts\ plug\ in\ zero\ for\ f(x)

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

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

Then set each factor equal to zero, if any of the ( ) equal zero, then the whole thing will equal zero because of the zero product rule. 

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

\displaystyle x=1\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x=-2\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x=5

 

 

Example Question #591 : Functions And Graphs

\displaystyle P(x) is a polynomial function. \displaystyle P(0) = 5\displaystyle P (1) = 15.

True or false: By the Intermediate Value Theorem, \displaystyle P(x) cannot have a zero on the interval \displaystyle (0,1 ).

Possible Answers:

False

True

Correct answer:

False

Explanation:

As a polynomial function, the graph of \displaystyle P(x) is continuous. By the Intermediate Value Theorem, if \displaystyle P(a) < M < P(b) or \displaystyle P(b) < M < P(a), then there must exist a value \displaystyle c \in (a,b) such that \displaystyle P(c)= M

Set \displaystyle a = 0 and \displaystyle b= 1. It is not true that \displaystyle P(0) < 0< P(1), so the Intermediate Value Theorem does not prove that there exists \displaystyle c \in (0,1 ) such that \displaystyle P(c)= 0. However, it does not disprove that such a value exists either. For example, observe the graphs below:

 Ivt

Both are polynomial graphs fitting the given conditions, but the only the equation graphed at right has a zero on \displaystyle c \in (0,1).

Example Question #42 : Polynomial Functions

How many \displaystyle x-intercepts does the graph of the function

\displaystyle f(x) = x^{2} + 7x - 9

have?

Possible Answers:

One

Zero

Two

Correct answer:

Two

Explanation:

The graph of a quadratic function \displaystyle f(x) has an \displaystyle x-intercept at any point \displaystyle (x,0 ) at which \displaystyle f(x) = 0, so we set the quadratic expression equal to 0:

\displaystyle x^{2} + 7x - 9 = 0

Since the question simply asks for the number of \displaystyle x-intercepts, it suffices to find the discriminant of the equation and to use it to determine this number. The discriminant of the quadratic equation 

\displaystyle ax^{2} + bx+ c = 0

is 

\displaystyle b^{2} - 4ac.

Set \displaystyle a = 1, b= 7, c = -9, and evaluate:

\displaystyle b^{2} - 4ac = 7^{2} - 4 (1)(-9)= 49 - (-36) =49 + 36 = 85

The discriminant is positive, so the \displaystyle f(x) has two real zeroes - and its graph has two \displaystyle x-intercepts.

Example Question #11 : Graphing Polynomial Functions

The vertex of the graph of the function 

\displaystyle f(x)= -4x^{2}+ 12x - 9

appears ________

Possible Answers:

in Quadrant III.

on an axis.

in Quadrant II.

in Quadrant I.

in Quadrant IV.

Correct answer:

on an axis.

Explanation:

The graph of the quadratic function \displaystyle f(x) = ax^{2} + bx+ c is a parabola with its vertex at the point with coordinates

\displaystyle \left ( -\frac{b}{2a}, f \left (-\frac{b}{2a} \right ) \right ).

Set \displaystyle a = -4, b = 12; the \displaystyle x-coordinate is 

\displaystyle -\frac{b}{2a} = - \frac{12}{2 \cdot (-4)} = - \frac{12}{-8} = \frac{3}{2} = 1\frac{1}{2}

Evaluate \displaystyle f \left ( \frac{3}{2} \right ) by substitution:

\displaystyle f \left ( \frac{3}{2} \right )= -4 \left ( \frac{3}{2} \right )^{2}+ 12 \left ( \frac{3}{2} \right ) - 9

\displaystyle = -4 \left ( \frac{9}{4} \right ) + 12 \left ( \frac{3}{2} \right ) - 9

\displaystyle = -9 +18 - 9

\displaystyle = 0

The vertex has 0 as its \displaystyle y-coordinate; it is therefore on an axis.

Example Question #43 : Polynomial Functions

\displaystyle P(x) is a polynomial function. \displaystyle P(0) = -5\displaystyle P (1) = 17.

True, false, or undetermined: \displaystyle P(x) has a zero on the interval \displaystyle (0,1 ).

Possible Answers:

Undetermined

True

False

Correct answer:

True

Explanation:

As a polynomial function, the graph of \displaystyle P(x) is continuous. By the Intermediate Value Theorem (IVT), if \displaystyle P(a) < M < P(b) or \displaystyle P(b) < M < P(a), then there must exist a value \displaystyle c \in (a,b) such that \displaystyle P(c)= M.

Setting \displaystyle M = 0, a = 0, b=1,  and examining the first condition, the above becomes:

if \displaystyle P(0) < 0 < P(1), then there must exist a value \displaystyle c \in (0, 1) such that \displaystyle P(c)= 0 - or, restated, \displaystyle P(x) must have a zero on the interval \displaystyle (0,1 ). Since \displaystyle P(0) = -5\displaystyle P (1) = 17. the condition holds, and by the IVT, it follows that \displaystyle P(x) has a zero on \displaystyle (0,1 ).

Example Question #591 : Functions And Graphs

\displaystyle P(x) is a polynomial function. The graph of \displaystyle P(x) has no \displaystyle x-intercepts; its \displaystyle y-intercept of the graph is at \displaystyle (0, 17).

True or false: By the Intermediate Value Theorem, \displaystyle P(x) has no negative values.

Possible Answers:

True

False

Correct answer:

True

Explanation:

As a polynomial function, the graph of \displaystyle P(x) is continuous. By the Intermediate Value Theorem, if \displaystyle P(a) < M < P(b) or \displaystyle P(b) < M < P(a), then there must exist a value \displaystyle c \in (a,b) such that \displaystyle P(c)= M.

Setting \displaystyle a= 0 and \displaystyle M = 0, assuming for now that \displaystyle b > 0, and looking only at the second condition, this statement becomes: If \displaystyle P(b) < 0 < P(a), then there must exist a value \displaystyle c \in (0, b) such that \displaystyle P(c)= 0 - or, equivalently, \displaystyle P(x) must have a zero on \displaystyle (0, b).

However, the conclusion of this statement is false: \displaystyle P(x) has no zeroes at all. Therefore, \displaystyle P(b) < 0 is false, and \displaystyle P(x) has no negative values for any \displaystyle x >0. By similar reasoning, \displaystyle P(x) has no negative values for any \displaystyle x< 0. Therefore, by the IVT, by way of its contrapositive, we have proved that \displaystyle P(x) is positive everywhere.

Example Question #11 : Graphing Polynomial Functions

Screen_shot_2014-12-24_at_2.27.32_pm

Which of the following is an equation for the above parabola?

Possible Answers:

\displaystyle y=(x-2)(x+3)

\displaystyle y=\frac{1}{2}(x+3)(x-2)

\displaystyle y=(x-3)(x+2)

\displaystyle y=\frac{1}{2}(x-3)(x+2)

Correct answer:

\displaystyle y=\frac{1}{2}(x-3)(x+2)

Explanation:

The zeros of the parabola are at \displaystyle 3 and \displaystyle -2, so when placed into the formula 

\displaystyle y=C(x-z_{1})(x-z_{2})

each of their signs is reversed to end up with the correct sign in the answer. The coefficient can be found by plugging in any easily-identifiable, non-zero point to the above formula. For example, we can plug in \displaystyle (4,3) which gives 

\displaystyle 3=C(4-3)(4+2)  

\displaystyle 6C=3

\displaystyle C=\frac{1}{2}

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