Algebra 1 : Functions and Lines

Study concepts, example questions & explanations for Algebra 1

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Example Questions

Example Question #11 : How To Find The Equation Of A Line

What is the slope and y-intercept of \displaystyle 2y-4x=12?

Possible Answers:

Slope: \displaystyle 6; y-intercept: \displaystyle 2

None of the other answers

Slope: \displaystyle 12; y-intercept: \displaystyle 4

Slope: \displaystyle 2; y-intercept: \displaystyle 6

Slope: \displaystyle 4; y-intercept: \displaystyle 12

Correct answer:

Slope: \displaystyle 2; y-intercept: \displaystyle 6

Explanation:

The easiest way to determine the slope and y-intercept of a line is by rearranging its equation to the \displaystyle y=mx+b form. In this form, the slope is the \displaystyle m and the y-intercept is the \displaystyle b.

Rearranging \displaystyle 2y-4x=12

gives you

\displaystyle y=2x+6

which has an \displaystyle m of 2 and a \displaystyle b of 6.

Example Question #351 : Functions And Lines

Find the equation of the line, in \displaystyle y=mx+b form, that contains the points \displaystyle (1,6), \displaystyle (11,12), and \displaystyle (-9,0).

Possible Answers:

\displaystyle y = \frac{3}{5}x - 7

\displaystyle y = 10x - 4

\displaystyle y = 3x +5

\displaystyle y=\frac{3}{5}x +\frac{27}{5}

\displaystyle y = \frac{5}{3}x + \frac{13}{3}

Correct answer:

\displaystyle y=\frac{3}{5}x +\frac{27}{5}

Explanation:

When finding the equation of a line given two or more points, the first step is to find the slope of that line. We can use the slope equation, \displaystyle \frac{y_{2}-y_{_{1}}}{x_{2}-x_{1}}. Any combination of the three points can be used, but let's consider the first two points, \displaystyle (1,6) and \displaystyle (11,12).

 \displaystyle \frac{12-6}{11-1} = \frac{3}{5}

So \displaystyle \frac{3}{5} is our slope.

Now, we have the half-finished equation

 \displaystyle y = \frac{3}{5}x + b

and we can complete it by plugging in the \displaystyle x and \displaystyle y values of any point. Let's use \displaystyle (1,6).

Solving

 \displaystyle 6 = \frac{3}{5}(1)+b 

for \displaystyle b gives us

 \displaystyle b = 6 - \frac{3}{5}

so

 \displaystyle b = 5\frac{2}{5} = \frac{27}{5}

We now have our completed equation: 

\displaystyle y = \frac{3}{5}x + \frac{27}{5}

Example Question #13 : How To Find The Equation Of A Line

We have two points: \displaystyle (-3,-1) and \displaystyle (4,9).

If these two points are connected by a straight line, find the equation describing this straight line.

Possible Answers:

\displaystyle y=-\frac{10}{3}x+\frac{3}{7}

\displaystyle y=\frac{10}{7}x+\frac{23}{7}

\displaystyle y=\frac{9}{2}x-\frac{3}{2}

None of these

\displaystyle y=\frac{10}{3}x+\frac{3}{7}

Correct answer:

\displaystyle y=\frac{10}{7}x+\frac{23}{7}

Explanation:

We need to find the equation of the line in slope-intercept form.

\displaystyle y=mx+b

In this formula, \displaystyle m is equal to the slope and \displaystyle b is equal to the y-intercept.

To find this equation, first, we need to find the slope by using the formula for the slope between two point.

\displaystyle m=\frac{y_2-y_1}{x_2-x_1}

In the formula, the points are \displaystyle (x_1,y_1) and \displaystyle (x_2,y_2).  In our case, the points are \displaystyle (-3,-1) and \displaystyle (4,9). Using our values allows us to solve for the slope.

\displaystyle m=\frac{9-(-1)}{4-(-3)}=\frac{10}{7}

We can replace the variable \displaystyle m with our new slope.

\displaystyle y=\frac{10}{7}x+b

Next, we need to find the y-intercept. To find this intercept, we can pick one of our given points and use it in the formula.

\displaystyle (-3,-1)

\displaystyle -1=\frac{10}{7}(-3)+b

Solve for \displaystyle b.

\displaystyle -1=\frac{-30}{7}+b

\displaystyle b=-1+\frac{30}{7}

\displaystyle b=\frac{23}{7}

Now, the final equation connecting the two points can be written using the new value for the y-intercept.

\displaystyle y=\frac{10}{7}x+\frac{23}{7}

Example Question #14 : How To Find The Equation Of A Line

Which of these lines has a slope of \displaystyle -3 and a y-intercept of \displaystyle 4?

Possible Answers:

\displaystyle y=-4x+3

\displaystyle y=-3x+4

\displaystyle y=4x-3

None of the other answers

\displaystyle y=3x-4

Correct answer:

\displaystyle y=-3x+4

Explanation:

Since all of the answers are in the \displaystyle y=mx+b form, the slope of each line is indicated by its \displaystyle m and its y-intercept is indicated by its \displaystyle b. Thus, a line with a slope of \displaystyle -3 and a y-intercept of \displaystyle 4 must have an equation of \displaystyle y=-3x+4.

Example Question #3635 : Algebra 1

Find the domain of:

 

\displaystyle \sqrt{2x-5}

Possible Answers:

\displaystyle \left \{ x|x= \frac{5}{2} \right \}

\displaystyle \left \{ x|-\infty < x< \infty \right \}

\displaystyle \left \{ x|x\neq \frac{5}{2} \right \}

\displaystyle \left \{ x|x\leq \frac{5}{2} \right \}

\displaystyle \left \{ x|x\geq \frac{5}{2} \right \}

Correct answer:

\displaystyle \left \{ x|x\geq \frac{5}{2} \right \}

Explanation:

The expression under the radical must be \displaystyle \geq 0.  Hence

\displaystyle \sqrt{2x-5} \geq 0

 

Solving for \displaystyle x, we get

\displaystyle x\geq \frac{5}{2}

Example Question #3641 : Algebra 1

Give, in slope-intercept form, the equation of a line through the points \displaystyle (-2, 5) and \displaystyle (-3, 8).

Possible Answers:

\displaystyle y = -3x +5

\displaystyle y = -3x -7

\displaystyle y = -\frac{1}{3}x +8

\displaystyle y = -3x -1

\displaystyle y = -\frac{1}{3}x -\frac{1}{3}

Correct answer:

\displaystyle y = -3x -1

Explanation:

First, use the slope formula to find the slope, setting \displaystyle x_{1} = -2, y_{1} = 5,x_{2} = -3, y_{2} = 8.

\displaystyle m = \frac{y _{2} - y_{1}}{x _{2} - x_{1}} = \frac{8 -5 }{-3-(-2)} = \frac{3 }{-1} = -3

We can write the equation in slope-intercept form as

\displaystyle y = mx + b.

Replace \displaystyle m = -3:

\displaystyle y = -3x + b

We can find \displaystyle b by substituting for \displaystyle x,y using either point - we will choose \displaystyle (-2, 5):

\displaystyle 5= -3 (-2) + b

\displaystyle 5= 6 + b

\displaystyle 5-6 = 6 -6 + b

\displaystyle b = -1

The equation is \displaystyle y = -3x -1.

Example Question #3642 : Algebra 1

Give, in slope-intercept form, the equation of a line through the points \displaystyle \left (3.5, 5.5 \right ) and \displaystyle (5.5, -2.5).

Possible Answers:

\displaystyle y = -4x + 3.5

\displaystyle y = -4x + 2.5

\displaystyle y = -0.25x + 13.5

\displaystyle y = -4x + 19.5

\displaystyle y = -0.25x + 5.5

Correct answer:

\displaystyle y = -4x + 19.5

Explanation:

First, use the slope formula to find the slope, setting \displaystyle x_{1} = 3.5, y_{1} = 5.5,x_{2} = 5.5, y_{2} = -2.5.

\displaystyle m = \frac{y _{2} - y_{1}}{x _{2} - x_{1}} = \frac{-2.5 -5.5}{5.5-3.5} = \frac{-8 }{2} = -4

We can write the equation in slope-intercept form as

\displaystyle y = mx + b.

Replace \displaystyle m = -4:

\displaystyle y = -4x + b

We can find \displaystyle b by substituting for \displaystyle x,y using either point - we will choose \displaystyle (3.5, 5.5):

\displaystyle 5.5= -4 (3.5) + b

\displaystyle 5.5= -14 +b

\displaystyle 5.5+14 = -14 +14+b

\displaystyle b = 19.5

The equation is \displaystyle y = -4x + 19.5.

Example Question #21 : How To Find The Equation Of A Line

Find the equation of the line that is parallel to \displaystyle y=3x+2 and contains the point (0,1).

Possible Answers:

\displaystyle y=-3x-1

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

\displaystyle y=\frac{1}{3}x-1

\displaystyle y=3x+1

Correct answer:

\displaystyle y=3x+1

Explanation:

To find the equation of a line, we need to know the slope and a point that passes through the line.  We can then use the equation \displaystyle y-y_1=m(x-x_1) where m is the slope of the line, and \displaystyle (x_{1}, y_{1}) a point on the line.  For parallel lines, the slopes are the same.  The slope of \displaystyle y=3x+2 is 3, so the slope of the parallel line will be 3 as well.  We know that the parallel line needs to contain the point (0,1), so we have all of the information we need.  We can now use the equation \displaystyle y-y_1=m(x-x_1)\Rightarrow y-1=3(x-0)\Rightarrow y=3x+1.

Example Question #21 : Slope And Line Equations

Write an equation in the form \displaystyle y=mx+b for the line that fits the following points:

(4,3), (6,6), (10,12)

Possible Answers:

\displaystyle y=3x-3

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

\displaystyle y=\frac{5}{2}x-2

\displaystyle y=\frac{2}{5}x-3

\displaystyle y=\frac{3}{2}x-3

Correct answer:

\displaystyle y=\frac{3}{2}x-3

Explanation:

The equation of a line is written in the following format: 

\displaystyle y=mx+b

1) The first step, then, is to find the slope, \displaystyle m.

\displaystyle m is equal to the change in \displaystyle y divided by the change in \displaystyle x.

So,

\displaystyle \frac{6-3}{6-4}=\frac{3}{2}

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

2) Next step is to find \displaystyle b. We can find values for \displaystyle x and \displaystyle y from any one of the given points, plug them in, and solve for \displaystyle b.

Let's use (4,3)

So, 

\displaystyle 3=\frac{3}{2}(4)+b

\displaystyle 3=6+b

\displaystyle b=-3

Then we just fill in our value for \displaystyle b, and we have \displaystyle y as a function of \displaystyle x.

\displaystyle y=\frac{3}{2}x-3

Example Question #354 : Functions And Lines

Which of these lines has a slope of 4 and a y-intercept of 6?

Possible Answers:

None of the other answers

\displaystyle 6y+4x=10

\displaystyle y=6x+4

\displaystyle y=2x+3

\displaystyle y=4x+6

Correct answer:

\displaystyle y=4x+6

Explanation:

When an equation is in the \displaystyle y=mx+b form, its slope is \displaystyle m and its y-intercept is \displaystyle b. Thus, we need an equation with an \displaystyle m of 4 and a \displaystyle b of 6, which would be 

\displaystyle y=4x+6

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