SSAT Upper Level Math : Other Lines

Study concepts, example questions & explanations for SSAT Upper Level Math

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Example Questions

Example Question #61 : Coordinate Geometry

Given the graph of the line below, find the equation of the line.

 

Act_math_160_04

Possible Answers:

\(\displaystyle y=\frac{10}{3}x-4\)

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

\(\displaystyle y=-x\)

\(\displaystyle y=x-4\)

Correct answer:

\(\displaystyle y=\frac{10}{3}x-4\)

Explanation:

To solve this question, you could use two points such as (1.2,0) and (0,-4) to calculate the slope which is 10/3 and then read the y-intercept off the graph, which is -4.

 

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

Which line passes through the points (0, 6) and (4, 0)?

Possible Answers:

y = –3/2 – 3

y = –3/2x + 6

y = 2/3x –6

y = 1/5x + 3

y = 2/3 + 5

Correct answer:

y = –3/2x + 6

Explanation:

P1 (0, 6) and P2 (4, 0)

First, calculate the slope:  m = rise ÷ run = (y2 – y1)/(x– x1), so m = –3/2

Second, plug the slope and one point into the slope-intercept formula: 

y = mx + b, so 0 = –3/2(4) + b and b = 6

Thus, y = –3/2x + 6

Example Question #3 : Other Lines

What line goes through the points (1, 3) and (3, 6)?

Possible Answers:

2x – 3y = 5

3x + 5y = 2

–2x + 2y = 3

4x – 5y = 4

–3x + 2y = 3

Correct answer:

–3x + 2y = 3

Explanation:

If P1(1, 3) and P2(3, 6), then calculate the slope by m = rise/run = (y2 – y1)/(x2 – x1) = 3/2

Use the slope and one point to calculate the intercept using y = mx + b

Then convert the slope-intercept form into standard form.

Example Question #61 : Coordinate Geometry

What is the slope-intercept form of \dpi{100} \small 8x-2y-12=0\(\displaystyle \dpi{100} \small 8x-2y-12=0\)?

Possible Answers:

\dpi{100} \small y=-2x+3\(\displaystyle \dpi{100} \small y=-2x+3\)

\dpi{100} \small y=-4x+6\(\displaystyle \dpi{100} \small y=-4x+6\)

\dpi{100} \small y=4x+6\(\displaystyle \dpi{100} \small y=4x+6\)

\dpi{100} \small y=2x-3\(\displaystyle \dpi{100} \small y=2x-3\)

\dpi{100} \small y=4x-6\(\displaystyle \dpi{100} \small y=4x-6\)

Correct answer:

\dpi{100} \small y=4x-6\(\displaystyle \dpi{100} \small y=4x-6\)

Explanation:

The slope intercept form states that \dpi{100} \small y=mx+b\(\displaystyle \dpi{100} \small y=mx+b\). In order to convert the equation to the slope intercept form, isolate \dpi{100} \small y\(\displaystyle \dpi{100} \small y\) on the left side:

\dpi{100} \small 8x-2y=12\(\displaystyle \dpi{100} \small 8x-2y=12\)

\dpi{100} \small -2y=-8x+12\(\displaystyle \dpi{100} \small -2y=-8x+12\)

\dpi{100} \small y=4x-6\(\displaystyle \dpi{100} \small y=4x-6\)

Example Question #1 : Lines

A line is defined by the following equation:

\(\displaystyle 7x+28y=84\)

What is the slope of that line?

Possible Answers:

\(\displaystyle \frac{1}{4}\)

\(\displaystyle 28\)

\(\displaystyle -\frac{1}{4}\)

\(\displaystyle -4\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle -\frac{1}{4}\)

Explanation:

The equation of a line is

y=mx + b where m is the slope

Rearrange the equation to match this:

7x + 28y = 84

28y = -7x + 84

y = -(7/28)x + 84/28

y = -(1/4)x + 3

m = -1/4

Example Question #142 : Lines

If the coordinates (3, 14) and (5, 15) are on the same line, what is the equation of the line?

Possible Answers:

\(\displaystyle y=-8x+38\)

\(\displaystyle y=-8x-38\)

\(\displaystyle y=\frac{1}{8}x+14.375\)

\(\displaystyle y=-\frac{1}{8}x+13.625\)

\(\displaystyle y=-\frac{1}{8}x+14.375\)

Correct answer:

\(\displaystyle y=-\frac{1}{8}x+14.375\)

Explanation:

First solve for the slope of the line, m using y=mx+b

m = (y2 – y1) / (x2 – x1)

= (15  14) / (5 3)

= (1 )/( 8)

=1/8

y = (1/8)x + b

Now, choose one of the coordinates and solve for b:

14 = (1/8)3 + b

14 = 3/8 + b

b = 14 + (3/8)

b = 14.375

y = (1/8)x + 14.375

Example Question #52 : Other Lines

What is the equation of a line that passes through coordinates \dpi{100} \small (2,6)\(\displaystyle \dpi{100} \small (2,6)\) and \dpi{100} \small (3,5)\(\displaystyle \dpi{100} \small (3,5)\)?

Possible Answers:

\dpi{100} \small y=2x-4\(\displaystyle \dpi{100} \small y=2x-4\)

\dpi{100} \small y=x+7\(\displaystyle \dpi{100} \small y=x+7\)

\dpi{100} \small y=2x+4\(\displaystyle \dpi{100} \small y=2x+4\)

\dpi{100} \small y=-x+8\(\displaystyle \dpi{100} \small y=-x+8\)

\dpi{100} \small y=3x+2\(\displaystyle \dpi{100} \small y=3x+2\)

Correct answer:

\dpi{100} \small y=-x+8\(\displaystyle \dpi{100} \small y=-x+8\)

Explanation:

Our first step will be to determing the slope of the line that connects the given points.

\(\displaystyle m=\frac{y_2-y_1}{x_2-x_1}=\frac{6-5}{2-3}=\frac{1}{-1}=-1\)

Our slope will be \(\displaystyle -1\). Using slope-intercept form, our equation will be \(\displaystyle y=(-1)x+b\). Use one of the give points in this equation to solve for the y-intercept. We will use \dpi{100} \small (2,6)\(\displaystyle \dpi{100} \small (2,6)\).

\(\displaystyle 6=(-1)(2)+b\)

\(\displaystyle 6=-2+b\)

\(\displaystyle 8=b\)

Now that we know the y-intercept, we can plug it back into the slope-intercept formula with the slope that we found earlier.

\(\displaystyle y=(-1)x+8\)

\(\displaystyle y=-x+8\)

This is our final answer.

Example Question #1 : How To Find The Equation Of A Line

Which of the following equations does NOT represent a line?

Possible Answers:

\(\displaystyle 5y=10\)

\(\displaystyle x-y=10\)

\(\displaystyle x^2+y=10\)

\(\displaystyle x+y=10\)

\(\displaystyle x=10\)

Correct answer:

\(\displaystyle x^2+y=10\)

Explanation:

The answer is \(\displaystyle x^2+y=10\).

A line can only be represented in the form \(\displaystyle x=z\) or \(\displaystyle y=mx+b\), for appropriate constants \(\displaystyle z\), \(\displaystyle m\), and \(\displaystyle b\). A graph must have an equation that can be put into one of these forms to be a line.

\(\displaystyle x^2+y=10\) represents a parabola, not a line. Lines will never contain an \(\displaystyle x^2\) term.

Example Question #9 : Other Lines

Let y = 3x – 6.

At what point does the line above intersect the following:

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

 

 

Possible Answers:

(–5,6)

They intersect at all points

(–3,–3)

(0,–1)

They do not intersect

Correct answer:

They intersect at all points

Explanation:

If we rearrange the second equation it is the same as the first equation. They are the same line.

Example Question #9 : Coordinate Geometry

A line has a slope of \(\displaystyle 2\) and passes through the point \(\displaystyle (8, 1)\). Find the equation of the line.

Possible Answers:

\(\displaystyle y=2x-10\)

\(\displaystyle y=15x+2\)

\(\displaystyle y=2x+1\)

\(\displaystyle y=2x-15\)

Correct answer:

\(\displaystyle y=2x-15\)

Explanation:

In finding the equation of the line given its slope and a point through which it passes, we can use the slope-intercept form of the equation of a line:

\(\displaystyle y=mx+b\), where \(\displaystyle m\) is the slope of the line and \(\displaystyle b\) is its \(\displaystyle y\)-intercept.

Plug the given conditions into the equation to find the \(\displaystyle y\)-intercept.

\(\displaystyle 1=2(8)+b\)

Multiply:

\(\displaystyle b+16=1\)

Subtract \(\displaystyle 16\) from each side of the equation:

\(\displaystyle b=-15\)

Now that you have solved for \(\displaystyle b\), you can write out the full equation of the line:

\(\displaystyle y=2x-15\)

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