Precalculus : Graphing Functions

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Graphing Functions

Information about the Hardy Weinberg equation: http://www.nature.com/scitable/definition/hardy-weinberg-equation-299

The Hardy Weinberg equation is a very important concept in population genetics. Suppose we have two "alleles" for a specific trait (like eye color, gender, etc..)  The proportion for which allele is present is given by \(\displaystyle x\) and \(\displaystyle y\)

Then by Hardy-Weinberg:

\(\displaystyle (x+y)^2 = 1\) , where both \(\displaystyle x\) and \(\displaystyle y\) are non-negative.

Which statement discribes the graph that would appropriately represents the above relation?

Possible Answers:

Curved line passing through the point \(\displaystyle (0.6, 0.9)\)

Straight line passing through the point \(\displaystyle (0.5, 0.5)\)

Parabola opening up passing through the point \(\displaystyle (1, 0.5)\)

Straight line passing through the point \(\displaystyle (0.5, 1)\)

Correct answer:

Straight line passing through the point \(\displaystyle (0.5, 0.5)\)

Explanation:

The equation can be reduced by taking the square root of both sides. 

\(\displaystyle (x+y)^2 = 1\) 

\(\displaystyle (x+y) = 1\) 

\(\displaystyle y = 1 - x\)

As a simple test, all other values when substituted into the original equation fail.  However, \(\displaystyle (0.5 + 0.5)^2 = 1\) works. Therefore \(\displaystyle (0.5,0.5)\) is our answer.

 

 

Example Question #1 : Graphing Functions

What is the y-intercept of the following equation?

\(\displaystyle f(x)=4\sin{3x}+2\)

Possible Answers:

\(\displaystyle (0,2)\)

\(\displaystyle (2,0)\)

\(\displaystyle (0,4)\)

\(\displaystyle (0,3)\)

\(\displaystyle (4,0)\)

Correct answer:

\(\displaystyle (0,2)\)

Explanation:

The y-intercept can by found by solving the equation when x=0. Thus,

\(\displaystyle f(0)=4\sin(3*0)+2\)

\(\displaystyle f(0)=4*0+2\)

\(\displaystyle f(0)=2\)

Example Question #2 : Graphing Functions

Determine the y intercept of \(\displaystyle f(x)\), where \(\displaystyle f(x)=\frac{x-4}{x^{2}+x-12}\) .

Possible Answers:

\(\displaystyle \bigg(\frac{1}{3},0\bigg)\)

\(\displaystyle (4,0)\)

\(\displaystyle (12,0)\)

\(\displaystyle (0,12)\)

\(\displaystyle \bigg(0,\frac{1}{3}\bigg)\)

Correct answer:

\(\displaystyle \bigg(0,\frac{1}{3}\bigg)\)

Explanation:

In order to determine the y-intercept of \(\displaystyle f(x)\), set \(\displaystyle x=0\)

\(\displaystyle f(0)=\frac{0-4}{0^{2}+0-12}\)

\(\displaystyle f(0)=\frac{-4}{-12}\)

\(\displaystyle f(0)=\frac{1}{3}\)

Solving for y, when x is equal to zero provides you with the y coordinate for the intercept. Thus the y-intercept is \(\displaystyle \bigg(0,\frac{1}{3}\bigg)\).

Example Question #2 : Graphing Functions

What is the \(\displaystyle y\)-intercept of the function, 

\(\displaystyle f(x)=(x-2)^2+4\)?

Possible Answers:

\(\displaystyle 2\)

\(\displaystyle 0\)

\(\displaystyle -2\)

\(\displaystyle 8\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle 8\)

Explanation:

To find the \(\displaystyle y\)-intercept we need to find the cooresponding \(\displaystyle y\) value when \(\displaystyle x = 0\)

Substituting \(\displaystyle x = 0\) into our function we get the following:

\(\displaystyle f(0)=(0-2)^2+4\)

\(\displaystyle f(0)=4+4\)

\(\displaystyle f(0)=8\)

Therefore, our \(\displaystyle y\)-intercept is \(\displaystyle 8\).

Example Question #1 : Graphing Functions

What is the value of the \(\displaystyle y\)-intercept of \(\displaystyle f(x)=(2x+4)^2+5\)?

Possible Answers:

\(\displaystyle 11\)

\(\displaystyle 16\)

\(\displaystyle 5\)

The graph does not have a \(\displaystyle y\)-intercept

\(\displaystyle 21\)

Correct answer:

\(\displaystyle 21\)

Explanation:

To find the \(\displaystyle y\)-intercept we need to find the cooresponding \(\displaystyle y\) value when \(\displaystyle x=0\). Therefore, we substitute in \(\displaystyle x=0\) and solve:

\(\displaystyle f(0)=(2(0)+4)^2+5\)

\(\displaystyle f(0)=(0+4)^2+5\)

\(\displaystyle f(0)=16+5\)

\(\displaystyle f(0)=21\)

Example Question #3 : Graphing Functions

If \(\displaystyle f(x) = f(-x)\), what kind of symmetry does the function \(\displaystyle f(x)\) have?

Possible Answers:

Even Symmetry

No Symmetry

Odd Symmetry

Symmetry across the line y=x

Correct answer:

Even Symmetry

Explanation:

The definition of even symmetry is if \(\displaystyle f(x) = f(-x)\)

Example Question #3 : Graphing Functions

If \(\displaystyle f(-x)=-f(x)\), what kind of symmetry does \(\displaystyle f(x)\) have?

Possible Answers:

Even symmetry 

Symmetry across the line y=x

Odd symmetry

No symmetry

Correct answer:

Odd symmetry

Explanation:

\(\displaystyle f(-x)=-f(x)\) is the definition of odd symmetry

Example Question #4 : Graphing Functions

Solve for \(\displaystyle n\).

Question_2

(Figure not drawn to scale).

Possible Answers:

\(\displaystyle 14^o\)

\(\displaystyle 10^o\)

\(\displaystyle 8^o\)

\(\displaystyle 12^o\)

Correct answer:

\(\displaystyle 14^o\)

Explanation:

The angles are supplementary, therefore, the sum of the angles must equal \(\displaystyle 180^o\).

\(\displaystyle \small (4n+22^o)+(8n-10^o)=180^o\)

\(\displaystyle \small 4n+22^o+8n-10^o=180^o\)

\(\displaystyle \small 12n+12^o=180^o\)

\(\displaystyle \small 12n=168^o\)

\(\displaystyle \small n=14^o\)

Example Question #1 : Understanding Complementary And Suplmentary Angles

Are \(\displaystyle 129^{\circ}\) and \(\displaystyle 51^{\circ}\) supplementary angles?

Possible Answers:

No

Not enough information

Yes

Correct answer:

Yes

Explanation:

Since supplementary angles must add up to \(\displaystyle 180^{\circ}\), the given angles are indeed supplementary.

Example Question #5 : Graphing Functions

Solve for \(\displaystyle x\) and \(\displaystyle y\).

Question_3

(Figure not drawn to scale).

Possible Answers:

\(\displaystyle \small x=15^o;\ y=37.5^o\)

\(\displaystyle \small x=15^o;\ y=52.5^o\)

\(\displaystyle \small x=7.5^o;\ y=18.75^o\)

\(\displaystyle \small x=15^o;\ y=7.5^o\)

Correct answer:

\(\displaystyle \small x=15^o;\ y=37.5^o\)

Explanation:

The angles containing the variable \(\displaystyle x\) all reside along one line, therefore, their sum must be \(\displaystyle 180^o\).

\(\displaystyle \small 5x+4x+3x=180^o\)

\(\displaystyle \small 12x=180^o\)

\(\displaystyle \small x=15^o\)

Because \(\displaystyle 2y\) and \(\displaystyle 5x\) are opposite angles, they must be equal.

\(\displaystyle \small 2y=5x\)

\(\displaystyle \small x=15^o\)

\(\displaystyle \small 2y=5(15^o)=75^o\)

\(\displaystyle \small y=\frac{75^o}{2}=37.5^o\)

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