Precalculus : Graph a Linear Function

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #3 : Linear Functions

Which of the following could be the function modeled by this graph?

Linearfxn

Possible Answers:

\displaystyle y=\frac{1}{5}x-7

\displaystyle y=5x+7

\displaystyle y=7x-5

\displaystyle y=5x-7

Correct answer:

\displaystyle y=5x-7

Explanation:

Which of the following could be the function modeled by this graph?

Linearfxn

We can begin here by trying to identify a couple points  on the graph

We can see that it crosses the y-axis at \displaystyle (0,-7)

Therefore, not only do we have a point, we have the y-intercept. This tells us that the equation of the line needs to have a \displaystyle -7 in it somewhere. Eliminate any option that do not have this feature.

Next, find the slope by counting up and over from the y-intercept to the next clear point.

It seems like the line goes up 5 and right 1 to the point \displaystyle (1,-2)

This means we have a slope of 5, which means our equation must look like this:

\displaystyle y=5x-7

 

Example Question #1 : Linear Functions

Find the slope of the linear function

\displaystyle y-3=5(x+2)

Possible Answers:

\displaystyle m=2

\displaystyle m=5

\displaystyle m=3

\displaystyle m=-3

Correct answer:

\displaystyle m=5

Explanation:

For the linear function in point-slope form

\displaystyle y-y_{1}=m\left ( x-x_{1}\right )

The slope is equal to \displaystyle m.

For this problem

\displaystyle y-3=5(x+2)

we get

\displaystyle m=5

Example Question #1 : Graph A Linear Function

Find the slope of the linear function

\displaystyle y-7=10(x+1)

Possible Answers:

\displaystyle m=-7

\displaystyle m=10

\displaystyle m=1

\displaystyle m=7

Correct answer:

\displaystyle m=10

Explanation:

For the linear function in point-slope form

\displaystyle y-y_{1}=m\left ( x-x_{1}\right )

The slope is equal to \displaystyle m.

For this problem

\displaystyle y-7=10(x+1)

we get

\displaystyle m=10

Example Question #6 : Linear Functions

What is the y-intercept of the line below? 

\displaystyle y = 3x + 4

Possible Answers:

\displaystyle (0, 4)

\displaystyle (4,0)

\displaystyle (0, -3)

\displaystyle (0, 3)

\displaystyle (3,0)

Correct answer:

\displaystyle (0, 4)

Explanation:

By definition, the y-intercept is the point on the line that crosses the y-axis. This can be found by substituting \displaystyle x = 0 into the equation. When we do this with our equation, 

\displaystyle y = 3x + 4 = 3\cdot0 + 4 = 0 + 4 = 4

Alternatively, you can remember \displaystyle y = mx + b form, a general form for a line in which \displaystyle m is the slope and \displaystyle b is the y-intercept. 

Example Question #7 : Linear Functions

What is the slope of the line below? 

\displaystyle y = \frac{2}{3}x + 6

Possible Answers:

\displaystyle 6

\displaystyle -6

\displaystyle \frac{1}{6}

\displaystyle -\frac{2}{3}

\displaystyle \frac{2}{3}

Correct answer:

\displaystyle \frac{2}{3}

Explanation:

Recall slope-intercept form, or \displaystyle y = mx + b. In this form, \displaystyle m is the slope and \displaystyle b is the y-intercept. Given our equation above, the slope must be the coefficient of the x, which is \displaystyle \frac{2}{3}

Example Question #8 : Linear Functions

What is the x-intercept of the equation below? 

\displaystyle y = 3x - 6

Possible Answers:

\displaystyle (0, -6)

\displaystyle (0, 2)

\displaystyle (-2, 0)

\displaystyle (\frac{1}{2}, 0)

\displaystyle (2,0)

Correct answer:

\displaystyle (2,0)

Explanation:

The x-intercept of an equation is the point at which the line crosses the x-axis. Thus, we can find the x-intercept by plugging in \displaystyle y=0. When we do this with our equation: 

\displaystyle y = 3x - 6 \rightarrow 0 = 3x - 6\rightarrow6 = 3x \rightarrow2 = x

Thus, our x-intercept is the point \displaystyle (2,0)

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