GMAT Math : Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #32 : Lines

A given line is defined by the equation \(\displaystyle y=\frac{1}{3}x+9\). What is the slope of any line parallel to this line?

Possible Answers:

\(\displaystyle -\frac{1}{3}\)

\(\displaystyle \frac{1}{3}\)

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

\(\displaystyle -3\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle \frac{1}{3}\)

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 \(\displaystyle y=\frac{1}{3}x+9\)\(\displaystyle m=\frac{1}{3}\) and therefore any line parallel to the given line must have a slope of \(\displaystyle \frac{1}{3}\).

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 #41 : Coordinate Geometry

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

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

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

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

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

Correct answer:

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

Explanation:

The parallel line has the equation \dpi{100} \small 4x-2y=5\(\displaystyle \dpi{100} \small 4x-2y=5\). 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\(\displaystyle \dpi{100} \small 4x-2y=5\) becomes \dpi{100} \small y=2x-\frac{5}{2}\(\displaystyle \dpi{100} \small y=2x-\frac{5}{2}\), so the slope is 2.

We know that our line must have an equation that looks like \dpi{100} \small y=2x+b\(\displaystyle \dpi{100} \small y=2x+b\). 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\(\displaystyle \dpi{100} \small y=2x-7\).

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 \(\displaystyle g(x)=2x-17\)

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