Algebra 1 : Algebra 1

Study concepts, example questions & explanations for Algebra 1

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Example Questions

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 

\(\displaystyle y=4x+6\)

Example Question #361 : Functions And Lines

Find the equation of the line with point \(\displaystyle \left ( -5,3 \right )\) and slope of \(\displaystyle 4\)

Possible Answers:

\(\displaystyle y=4x-23\)

\(\displaystyle y=4x-13\)

\(\displaystyle y=-4x+23\)

\(\displaystyle y=4x+23\)

Correct answer:

\(\displaystyle y=4x+23\)

Explanation:

Use the point-slope formula to find the equation:

\(\displaystyle Y-Y_{1}=M(X-X_{1})\)

\(\displaystyle y-3=4(x+5)\)

\(\displaystyle y-3 = 4x+20\)

\(\displaystyle y-3+3=4x+20+3\)

\(\displaystyle y=4x+23\)

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

Which of the following equations in standard form describes a line passing through the point \(\displaystyle \left ( -2,5 \right )\) with a slope of \(\displaystyle -3\ ?\)

Possible Answers:

\(\displaystyle -3x - 4y = - 1\)

\(\displaystyle -3x + y = 11\)

\(\displaystyle 3x + y = - 1\)

\(\displaystyle 3x + y = 11\)

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

Correct answer:

\(\displaystyle 3x + y = - 1\)

Explanation:

Start by using point-slope form:

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

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

Multiply the right side by the distributive property:

\(\displaystyle y-5 = -3x -6\) 

Then, convert to standard form:

\(\displaystyle 3x + y = - 1\)

Example Question #361 : Functions And Lines

Rewrite in slope-intercept form: \(\displaystyle 5x+20y=60\).

Possible Answers:

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

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

\(\displaystyle y=\frac{1}{4}x+3\)

\(\displaystyle y=-\frac{1}{4}x+3\)

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

Correct answer:

\(\displaystyle y=-\frac{1}{4}x+3\)

Explanation:

Slope-intercept form is \(\displaystyle y=mx+b\), where \(\displaystyle m\) is the slope and \(\displaystyle b\) is the y-intercept.  To rewrite the original equation in slope-intercept form, you must isolate the \(\displaystyle y\) variable: 

\(\displaystyle 5x+20y=60\)

\(\displaystyle -5x+20y=60-5x\)

\(\displaystyle 20y=-5x+60\)

Now, divide each side by 20 so that \(\displaystyle y\) stands alone and simplify, and you are left with the slope-intercept form of the equation:

\(\displaystyle y=-\frac{5}{20}x+\frac{60}{20}\)

\(\displaystyle y=-\frac{1}{4}x+3\)

Example Question #1 : Solving Functions

Find the equation for the line goes through the two points below.

\(\displaystyle (1,-2)\)

\(\displaystyle (-3, 6)\)

Possible Answers:

\(\displaystyle y = 2x -4\)

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

\(\displaystyle y = \frac{1}{2}x + 4\)

\(\displaystyle y = 4x - 2\)

\(\displaystyle y = -2x\)

Correct answer:

\(\displaystyle y = -2x\)

Explanation:

Let \(\displaystyle P_{1} = (1, \; -2) \; \; and \; \; P_{2} = (-3, \; 6)\).

First, calculate the slope between the two points.

\(\displaystyle m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}} = \frac{6 - (-2)}{-3 - 1} = \frac{8}{-4} = -2\)

Next, use the slope-intercept form to calculate the intercept. We are able to plug in our value for the slope, as well the the values for \(\displaystyle P_1\).

\(\displaystyle y = mx + b\)

\(\displaystyle -2 = -2(1) + b\)

\(\displaystyle b=0\)

Using slope-intercept form, where we know \(\displaystyle m=-2\) and \(\displaystyle b=0\), we can see that the equation for this line is \(\displaystyle y = -2x\).

Example Question #3643 : Algebra 1

What is the equation of the line connecting the points \(\displaystyle (-3,0)\) and \(\displaystyle (2,5)\)?

Possible Answers:

\(\displaystyle y=x-3\)

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

\(\displaystyle y=x+3\)

\(\displaystyle y=3x+1\)

Equation is undefined or does not exist.

Correct answer:

\(\displaystyle y=x+3\)

Explanation:

To find the equation of this line, we need to know its slope and y-intercept. Let's find the slope first using our general slope formula.

\(\displaystyle m=\frac{\Delta y}{\Delta x}=\frac{y_2-y_1}{x_2-x_1}\)

The points are \(\displaystyle (x_1,y_1)\) and \(\displaystyle (x_2,y_2)\).  In this case, our points are (–3,0) and (2,5). Therefore, we can calculate the slope as the following:

\(\displaystyle m=\frac{5-0}{2-(-3)}=\frac{5}{5}=1\)

Our slope is 1, so plug that into the equation of the line:

\(\displaystyle y=mx+b \,\,\, \rightarrow \,\,\,y=(1)x+b \,\,\, \rightarrow \,\,\, y=x+b\)

We still need to find b, the y-intercept. To find this, we pick one of our points (either (–3,0) or (2,5)) and plug it into our equation. We'll use (–3,0).

\(\displaystyle y=x+b\)

\(\displaystyle 0=-3+b\)

Solve for b.

\(\displaystyle b=3\)

The equation is therefore written as \(\displaystyle y=x+3\).

 

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