GMAT Math : Coordinate Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #3 : Calculating The Slope Of Parallel Lines

A given line is defined by the equation \displaystyle y=-5x+11. What is the slope of any line parallel to this line?

Possible Answers:

\displaystyle \frac{1}{5}

\displaystyle -\frac{1}{5}

\displaystyle 10

\displaystyle 5

\displaystyle -5

Correct answer:

\displaystyle -5

Explanation:

Any line that is parallel to a line \displaystyle y=mx+b has a slope that is equal to the slope \displaystyle m. Given \displaystyle y=-5x+11\displaystyle m=-5 and therefore any line parallel to the given line must have a slope of \displaystyle -5.

Example Question #1 : Calculating The Slope Of Parallel Lines

A given line is defined by the equation \displaystyle y=\frac{4}{3}x+12. What is the slope of any line parallel to this line?

Possible Answers:

\displaystyle 12

\displaystyle \frac{4}{3}

\displaystyle -\frac{4}{3}

\displaystyle \frac{3}{4}

\displaystyle -\frac{3}{4}

Correct answer:

\displaystyle \frac{4}{3}

Explanation:

Any line that is parallel to a line \displaystyle y=mx+b has a slope that is equal to the slope \displaystyle m. Given \displaystyle y=\frac{4}{3}x+12\displaystyle m=\frac{4}{3} and therefore any line parallel to the given line must have a slope of \displaystyle \frac{4}{3}.

Example Question #1 : Calculating The Equation Of A Parallel Line

What is the equation of the line that is parallel to \displaystyle y=2x+10 and goes through point \displaystyle (5,1)?

Possible Answers:

\displaystyle y=\frac{1}{2}x-9

\displaystyle y=2x-9

\displaystyle y=-\frac{1}{2}+9

\displaystyle y=-2x-9

Correct answer:

\displaystyle y=2x-9

Explanation:

Parallel lines have the same slope. Therefore, the slope of the new line is \displaystyle 2, as the equation of the original line is \displaystyle y=2x+10 \displaystyle (y=mx+b),with slope \displaystyle m.

\displaystyle m=2     and      \displaystyle (5,1):

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

\displaystyle y-1=2(x-5)

\displaystyle y-1=2x-10

\displaystyle y=2x-10+1

\displaystyle y=2x-9

Example Question #1 : Calculating The Equation Of A Parallel Line

Find the equation of a line that is parallel to \displaystyle 4x-2y=5 and passes through the point \displaystyle (4,1).

 

Possible Answers:

\dpi{100} \small y=-2x+7

\dpi{100} \small y=2x+7

\dpi{100} \small y=2x-7

\dpi{100} \small y=-2x-7

\dpi{100} \small y< 2x-7None of the answers are correct.

Correct answer:

\dpi{100} \small y=2x-7

Explanation:

The parallel line has the equation \dpi{100} \small 4x-2y=5. We can find the slope by putting the equation into slope-intercept form, y = mx + b, where m is the slope and b is the intercept.  \dpi{100} \small 4x-2y=5 becomes \dpi{100} \small y=2x-\frac{5}{2}, so the slope is 2.

We know that our line must have an equation that looks like \dpi{100} \small y=2x+b. Now we need the intercept. We can solve for b by plugging in the point (4, 1).

1 = 2(4) + b

b = –7

Then the line in question is \dpi{100} \small y=2x-7.

Example Question #3 : Calculating The Equation Of A Parallel Line

Given:

\displaystyle \small f(x)=4x+13

Which of the following is the equation of a line parallel to \displaystyle f(x) that has a y-intercept of \displaystyle -13?

Possible Answers:

\displaystyle \small \small \small f(x)=-\frac{1}{4}x-13

\displaystyle \small \small f(x)=-4x+13

\displaystyle \small \small \small f(x)=-\frac{1}{4}x+13

\displaystyle \small \small f(x)=\frac{1}{4}x+13

\displaystyle \small \small f(x)=4x-13

Correct answer:

\displaystyle \small \small f(x)=4x-13

Explanation:

Parallel lines have the same slope, so our slope will still be 4. The y-intercept is just the "+b" at the end. In f(x) the y-intercept is 13. In this case, we need to have a y-intercept of -13, so our equation just becomes:

\displaystyle \small \small f(x)=4x-13

Example Question #44 : Lines

Find the equation of the line that is parallel to the \displaystyle g(x) and passes through the point \displaystyle (8,9).

\displaystyle \small g(x)=6x+7

Possible Answers:

\displaystyle \small \small \small y=-\frac{1}{6}x-39

\displaystyle \small \small y=-6x-39

\displaystyle \small y=6x-39

\displaystyle \small \small y=\frac{1}{6}x-39

\displaystyle \small \small y=6x+39

Correct answer:

\displaystyle \small y=6x-39

Explanation:

Two lines are parallel if they have the same slope. The slope of g(x) is 6, so eliminate anything without a slope of 6.

Recall slope intercept form which is \displaystyle y=mx+b.

We know that the line must have an m of 6 and an (x,y) of (8,9). Plug everything in and go from there.

\displaystyle 9=(6\cdot 8)+b

\displaystyle \small 9=48+b

\displaystyle \small b=9-48=-39

So we get:

\displaystyle \small y=6x-39

Example Question #3 : Calculating The Equation Of A Parallel Line

Given the function \displaystyle f(x)=7x-12, which of the following is the equation of a line parallel to \displaystyle f(x) and has a \displaystyle y-intercept of \displaystyle 8?

Possible Answers:

\displaystyle g(x)=7x-8

\displaystyle g(x)=-\frac{1}{7}x+8

\displaystyle g(x)=\frac{1}{7}x+8

\displaystyle g(x)=-7x+2

\displaystyle g(x)=7x+8

Correct answer:

\displaystyle g(x)=7x+8

Explanation:

Given a line \displaystyle a defined by the equation \displaystyle f(x)=mx+b with slope \displaystyle m, any line that is parallel to \displaystyle a also has a slope of \displaystyle m. Since \displaystyle f(x)=7x-12, the slope \displaystyle m is \displaystyle 7 and the slope of any line \displaystyle g(x) parallel to \displaystyle f(x) also has a slope of \displaystyle m=7.

Since \displaystyle g(x) also needs to have a \displaystyle y-intercept of \displaystyle 8, then the equation for \displaystyle g(x) must be \displaystyle g(x)=7x+8

Example Question #16 : Parallel Lines

Given the function \displaystyle f(x)=-\frac{6}{5}x+7, which of the following is the equation of a line parallel to \displaystyle f(x) and has a \displaystyle y-intercept of \displaystyle -2?

Possible Answers:

\displaystyle g(x)=-\frac{6}{5}x-2

\displaystyle g(x)=\frac{5}{6}x-2

\displaystyle g(x)=-\frac{5}{6}x-2

\displaystyle g(x)=\frac{6}{5}x-2

\displaystyle g(x)=-\frac{6}{5}x+2

Correct answer:

\displaystyle g(x)=-\frac{6}{5}x-2

Explanation:

Given a line \displaystyle a defined by the equation \displaystyle f(x)=mx+b with slope \displaystyle m, any line that is parallel to \displaystyle a also has a slope of \displaystyle m. Since \displaystyle f(x)=-\frac{6}{5}x+7, the slope \displaystyle m is \displaystyle -\frac{6}{5} and the slope of any line \displaystyle g(x) parallel to \displaystyle f(x) also has a slope of \displaystyle m=-\frac{6}{5}.

Since \displaystyle g(x) also needs to have a \displaystyle y-intercept of \displaystyle -2, then the equation for \displaystyle g(x) must be \displaystyle g(x)=-\frac{6}{5}x-2

Example Question #45 : Lines

Given the function \displaystyle f(x)=2x+5, which of the following is the equation of a line parallel to \displaystyle f(x) and has a \displaystyle y-intercept of \displaystyle -17?

Possible Answers:

\displaystyle g(x)=-2x-17

\displaystyle g(x)=-2x+17

\displaystyle g(x)=-\frac{1}{2}x-17

\displaystyle g(x)=2x-17

\displaystyle g(x)=2x+17

Correct answer:

\displaystyle g(x)=2x-17

Explanation:

Given a line \displaystyle a defined by the equation \displaystyle f(x)=mx+b with slope \displaystyle m, any line that is parallel to \displaystyle a also has a slope of \displaystyle m. Since \displaystyle f(x)=2x+5, the slope \displaystyle m is \displaystyle 2 and the slope of any line \displaystyle g(x) parallel to \displaystyle f(x) also has a slope of \displaystyle m=2.

Since \displaystyle g(x) also needs to have a \displaystyle y-intercept of \displaystyle -17, then the equation for \displaystyle g(x) must be \displaystyle g(x)=2x-17

Example Question #42 : Coordinate Geometry

What is the equation of the line that is perpendicular to \displaystyle y=2x+10 and goes through point \displaystyle (5,1)?

Possible Answers:

\displaystyle y=\frac{1}{2}x+\frac{7}{2}

\displaystyle y=-2x+\frac{7}{2}

\displaystyle y=2x+\frac{7}{2}

\displaystyle y=-\frac{1}{2}x+\frac{7}{2}

Correct answer:

\displaystyle y=-\frac{1}{2}x+\frac{7}{2}

Explanation:

Perpendicular lines have slopes that are negative reciprocals of each other.

The slope for the given line is \displaystyle 2, from \displaystyle y=2x+10 \displaystyle (y=mx+b), where \displaystyle m is the slope. Therefore, the negative reciprocal is \displaystyle -\frac{1}{2}.

\displaystyle m=-\frac{1}{2}     and      \displaystyle (5,1):

 

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

\displaystyle y-1=-\frac{1}{2}(x-5)

\displaystyle y-1=-\frac{1}{2}x+\frac{5}{2}

\displaystyle y=-\frac{1}{2}x+\frac{5}{2}+1

\displaystyle y=-\frac{1}{2}x+\frac{5}{2}+\frac{2}{2}

\displaystyle y=-\frac{1}{2}x+\frac{7}{2}

 

 

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