GMAT Math : Coordinate Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #1 : Coordinate Geometry

Which of the following quadrants can contain the midpoint of a line segment with endpoints \(\displaystyle (0,A)\) and \(\displaystyle (-A,0)\) for some nonzero value of \(\displaystyle A\)?

Possible Answers:

Quadrants III and IV

Quadrants I and III

Quadrants II and III

Quadrants II and IV

Quadrants I and IV

Correct answer:

Quadrants II and IV

Explanation:

The midpoint of the line segment with endpoints \(\displaystyle (0,A)\) and \(\displaystyle (-A,0)\)  is \(\displaystyle \left ( \frac{0+ (-A) }{2}, \frac{A+ 0 }{2}, \right )\), or \(\displaystyle \left (- \frac{A }{2}, \frac{A }{2}, \right )\)

If \(\displaystyle A > 0\), then the \(\displaystyle x\)-coordinate is negative and the \(\displaystyle y\)-coordinate is positive, so the midpoint is in Quadrant II. If \(\displaystyle A < 0\), the reverse is true, so the midpoint is in Quadrant IV.

Example Question #2 : Coordinate Geometry

The midpoint of a line segment with endpoints \(\displaystyle (A + 2, 2B-1)\) and \(\displaystyle (B+4, 2A+1)\) is \(\displaystyle (8,10)\). Sove for \(\displaystyle B\).

Possible Answers:

\(\displaystyle 2\)

\(\displaystyle 8\)

It cannot be determined from the information given.

\(\displaystyle 5\)

\(\displaystyle 10\)

Correct answer:

It cannot be determined from the information given.

Explanation:

The midpoint of a line segment with endpoints \(\displaystyle (x_{1}, y_{1}), (x_{2}, y_{2})\) is 

\(\displaystyle \left ( \frac{x_{1}+x_{2} }{2},\frac{y_{1}+y_{2} }{2} \right )\).

Substitute the coordinates of the endpoints, then set each equation to the appropriate midpoint coordinate. 

\(\displaystyle x\)-coordinate:  \(\displaystyle \frac{(A + 2)+ (B + 4) }{2} = 8\)

\(\displaystyle y\)-coordinate: \(\displaystyle \frac{(2B-1)+(2A +1) }{2} = 10\)

 

Simplify each, then solve the system of linear equations in two variables:

 

\(\displaystyle \frac{(A + 2)+ (B + 4) }{2} = 8\)

\(\displaystyle \frac{(A + B + 6) }{2} = 8\)

\(\displaystyle A + B + 6 = 16\)

\(\displaystyle A + B = 10\)

 

\(\displaystyle \frac{(2B-1)+(2A +1) }{2} = 10\)

\(\displaystyle \frac{2A + 2B }{2} = 10\)

\(\displaystyle A + B = 10\)

 

The two linear equations turn out to be equivalent, meaning that there are infinitely many solutions to the system. Therefore, insufficient information is given to answer the question.

Example Question #1 : Coordinate Geometry

Find the midpoint of the points \(\displaystyle (2, 9)\) and \(\displaystyle (4, 3)\).

Possible Answers:

\(\displaystyle (6,12)\)

\(\displaystyle (2.5,5.5)\)

\(\displaystyle (2,5)\)

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

\(\displaystyle (3,6)\)

Correct answer:

\(\displaystyle (3,6)\)

Explanation:

Add the corresponding points together and divide both values by 2:

(\frac{2+4}{2},\frac{9+3}{2}) = (3, 6)\(\displaystyle (\frac{2+4}{2},\frac{9+3}{2}) = (3, 6)\)

Example Question #2 : Coordinate Geometry

What is the midpoint of \(\displaystyle (-5,1)\) and \(\displaystyle (1,4)\)?

Possible Answers:

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

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

\(\displaystyle (3,\frac{5}{2})\)

\(\displaystyle (2,\frac{5}{2})\)

\(\displaystyle (-2,\frac{5}{2})\)

Correct answer:

\(\displaystyle (-2,\frac{5}{2})\)

Explanation:

Add the x-values and divide by 2, and then add the y-values and divide by 2.  Be careful of the negatives!

\(\displaystyle (\frac{-5+1}{2},\frac{1+4}{2}) = (-2, \frac{5}{2})\)

Example Question #4 : Coordinate Geometry

Consider segment \(\displaystyle \overline{JK}\) which passes through the points \(\displaystyle \left ( 4,5\right )\) and \(\displaystyle \left ( 144,75\right )\).

What are the correct coordinates for the midpoint of \(\displaystyle \overline{JK}\)?

Possible Answers:

\(\displaystyle \small (74,40)\)

\(\displaystyle \small \small (74,35)\)

\(\displaystyle \small \small (75,45)\)

\(\displaystyle \small \small (73,42)\)

\(\displaystyle \small \small (70,35)\)

Correct answer:

\(\displaystyle \small (74,40)\)

Explanation:

Midpoint formula is as follows:

\(\displaystyle \small m=(\frac{x+x'}{2},\frac{y+y'}{2})\)

Plug in and calculate:

\(\displaystyle \small \small \small m=(\frac{4+144}{2},\frac{75+5}{2})=(74,40)\)

Example Question #4 : Coordinate Geometry

Segment \(\displaystyle YU\) has endpoints of \(\displaystyle (-6,8)\) and \(\displaystyle (4,26)\). If the midpoint of \(\displaystyle YU\) is given by point \(\displaystyle O\), what are the coordinates of point \(\displaystyle O\)?

Possible Answers:

\(\displaystyle (-1,17)\)

\(\displaystyle (17,-1)\)

\(\displaystyle (5,17)\)

\(\displaystyle (-5,-17)\)

\(\displaystyle (17,5)\)

Correct answer:

\(\displaystyle (-1,17)\)

Explanation:

Midpoints can be found using the following:

\(\displaystyle midpoint(x,y)=\left(\frac{x+x'}{2},\frac{y+y'}{2}\right)\)

Plug in our points (-6,8) and (4,26) to find the midpoint.

\(\displaystyle \small \small midpoint(x,y)=\left(\frac{-6+4}{2},\frac{8+26}{2}\right)=\left(\frac{-2}{2},\frac{34}{2}\right)=(-1,17)\)

Example Question #3 : Calculating The Midpoint Of A Line Segment

What are the coordinates of the mipdpoint of the line segment \(\displaystyle AB\) if \(\displaystyle A=(2,3)\) and \(\displaystyle B=(2,-7)?\)

Possible Answers:

\(\displaystyle (2,4)\)

\(\displaystyle (0,4)\)

\(\displaystyle (0,-10)\)

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

\(\displaystyle (0,-2)\)

Correct answer:

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

Explanation:

The midpoint formula is \(\displaystyle (\frac{x_{2}+x_{1}}{2},\frac{y_{2}+y_{1}}{2}) = (\frac{2+2}{2},\frac{3+-7}{2})=(2,-2).\)

Example Question #3 : Lines

The quadrilateral with vertices \(\displaystyle (0,0),(22,0), (16,4), (4,4)\) is a trapezoid. What are the endpoints of its midsegment?

Possible Answers:

\(\displaystyle (11,0),(10,4)\)

\(\displaystyle (2,2),(19,2 )\)

\(\displaystyle (0,0), (16,4)\)

\(\displaystyle (22,0), (4,4)\)

\(\displaystyle (0,2),(23,2 )\)

Correct answer:

\(\displaystyle (2,2),(19,2 )\)

Explanation:

The midsegment of a trapezoid is the segment whose endpoints are the midpoints of its legs - its nonparallel opposite sides. These two sides are the ones with endpoints \(\displaystyle (0,0), (4,4)\) and \(\displaystyle (22,0), (16,4)\). The midpoint of each can be found by taking the means of the \(\displaystyle x\)- and \(\displaystyle y\)-coordinates:

\(\displaystyle (0,0), (4,4): \left ( \frac{0+4}{2},\frac{0+4}{2} \right ) \Rightarrow (2,2)\)

\(\displaystyle (22,0), (16,4): \left ( \frac{22+16}{2},\frac{0+4}{2} \right ) \Rightarrow (19,2)\)

The midsegment is the segment that has endpoints (2,2) and (19,2)

Example Question #3 : Coordinate Geometry

The midpoint of a line segment with endpoints \(\displaystyle (2A, B)\) and \(\displaystyle (B + 7, 3A - 2)\) is \(\displaystyle (9, 6)\). What is \(\displaystyle A\)?

Possible Answers:

\(\displaystyle 7\)

It cannot be determined from the information given.

\(\displaystyle 5\)

\(\displaystyle 6\)

\(\displaystyle 3\)

Correct answer:

\(\displaystyle 3\)

Explanation:

If the midpoint of a line segment with endpoints \(\displaystyle (2A, B)\) and \(\displaystyle (B + 7, 3A - 2)\) is \(\displaystyle (9, 6)\), then by the midpoint formula, 

\(\displaystyle \frac{2A + (B + 7)}{2} = 9\) 

and

 \(\displaystyle \frac{B + (3A - 2)}{2} = 6\).

The first equation can be simplified as follows:

\(\displaystyle 2A + B + 7 = 18\) 

or 

\(\displaystyle 2A + B = 11\)

The second can be simplified as follows:

\(\displaystyle 3A + B - 2 = 12\)

or 

\(\displaystyle 3A + B = 14\)

This is a system of linear equations. \(\displaystyle A\) can be calculated by subtracting:

\(\displaystyle 3A + B = 14\)

\(\displaystyle \underline{2A + B = 11 }\)

\(\displaystyle A \; \; \; \; \; \; \; \; = 3\)

Example Question #5 : Lines

If the midpoint of \(\displaystyle \overline{VU}\) is \(\displaystyle \left ( 6,7\right )\) and \(\displaystyle \textup{Point }V\) is at \(\displaystyle \left (2,9\right )\), what are the coordinates of \(\displaystyle \textup{Point }U\)?

Possible Answers:

\(\displaystyle \left ( 10,5\right )\)

\(\displaystyle \left ( -5,10\right )\)

\(\displaystyle \left ( 5,10\right )\)

\(\displaystyle \left ( 14,23\right )\)

\(\displaystyle \left ( 23,14\right )\)

Correct answer:

\(\displaystyle \left ( 10,5\right )\)

Explanation:

Midpoint formula is as follows:

\(\displaystyle \small \small m(x,y)=(\frac{x+x'}{2},\frac{y+y'}{2})\)

In this case, we have x,y and the value of the midpoint. We need to findx' and y'

V is at (2,9) and the midpoint is at (6,7)

\(\displaystyle \small 6=\frac{2+x'}{2}\)                       and                               \(\displaystyle \small 7=\frac{9+y'}{2}\)

\(\displaystyle \small x'=6*2-2=10\)                         \(\displaystyle \small y'=7*2-9=14-9=5\)

 

So we have (10,5) as point U

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