Precalculus : Graph a Linear Function

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Graph A Linear Function

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

Linearfxn

Possible Answers:

\(\displaystyle y=7x-5\)

\(\displaystyle y=5x-7\)

\(\displaystyle y=5x+7\)

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

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 #2 : Linear Functions

Find the slope of the linear function

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

Possible Answers:

\(\displaystyle m=-3\)

\(\displaystyle m=5\)

\(\displaystyle m=3\)

\(\displaystyle m=2\)

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 #3 : Linear Functions

Find the slope of the linear function

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

Possible Answers:

\(\displaystyle m=10\)

\(\displaystyle m=7\)

\(\displaystyle m=-7\)

\(\displaystyle m=1\)

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 #3 : Graph A Linear Function

What is the y-intercept of the line below? 

\(\displaystyle y = 3x + 4\)

Possible Answers:

\(\displaystyle (0, 3)\)

\(\displaystyle (4,0)\)

\(\displaystyle (0, 4)\)

\(\displaystyle (0, -3)\)

\(\displaystyle (3,0)\)

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 #1 : Graph A Linear Function

What is the slope of the line below? 

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

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle \frac{2}{3}\)

\(\displaystyle \frac{1}{6}\)

\(\displaystyle -\frac{2}{3}\)

\(\displaystyle -6\)

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 #4 : Linear Functions

What is the x-intercept of the equation below? 

\(\displaystyle y = 3x - 6\)

Possible Answers:

\(\displaystyle (-2, 0)\)

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

\(\displaystyle (0, 2)\)

\(\displaystyle (0, -6)\)

\(\displaystyle (2,0)\)

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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