GMAT Math : Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #2 : Other Lines

Solve for \(\displaystyle x\) in the coordinate \(\displaystyle (x,1)\) on line \(\displaystyle 3y=4x+1\)?

Possible Answers:

\(\displaystyle -1\)

\(\displaystyle 1\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle \frac{1}{2}\)

Explanation:

To solve for \(\displaystyle x\) for \(\displaystyle y=1\), we have to plug 1 into the \(\displaystyle y\) variable of the equation and solve for \(\displaystyle x\):

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

\(\displaystyle 3(1)=4x+1\)

\(\displaystyle 3=4x+1\)

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

\(\displaystyle 2=4x\)

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

Example Question #3 : Calculating Whether Point Is On A Line With An Equation

Solve for \(\displaystyle y\) in the coordinate  \(\displaystyle (5,y)\) on line \(\displaystyle 14y-10x=20\)?

Possible Answers:

\(\displaystyle 70\)

\(\displaystyle 5\)

\(\displaystyle -5\)

\(\displaystyle -70\)

Correct answer:

\(\displaystyle 5\)

Explanation:

To solve for \(\displaystyle y\) for \(\displaystyle x=5\), we have to plug \(\displaystyle 5\) into the \(\displaystyle x\) variable of the equation and solve for \(\displaystyle y\):

\(\displaystyle 14y-10x=20\)

\(\displaystyle 14y-10(5)=20\)

\(\displaystyle 14y-50=20\)

\(\displaystyle 14y=20+50\)

\(\displaystyle 14y=70\)

\(\displaystyle y=5\)

Example Question #1 : Calculating Whether Point Is On A Line With An Equation

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

If the point \(\displaystyle \left ( 16,y\right )\) is on \(\displaystyle \overline{JK}\), what is the value of y?

Possible Answers:

\(\displaystyle -5\)

\(\displaystyle 5\)

\(\displaystyle 11\)

\(\displaystyle 0\)

\(\displaystyle -11\)

Correct answer:

\(\displaystyle 11\)

Explanation:

First, use the points to find the equation of JK:

Given that JK passes through (4,5) and (144,75) we can find the slope as follows:

Slope is found via:

\(\displaystyle m=\frac{y'-y}{x'-x}\)

Plug in and calculate:

\(\displaystyle \small \small m=\frac{75-5}{144-4}=\frac{70}{140}=\frac{1}{2}\)

Next, we need to use one of our points and the slope to find our y-intercept. I'll use (4,5).

\(\displaystyle \small 5=\frac{1}{2}*4+b\)

\(\displaystyle \small b=5-2=3\)

So our answer is: 

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

To find y, we need to plug in 16 for x and solve:

 

\(\displaystyle \small \small y=\frac{16}{2}+3=8+3=11\)

Example Question #4 : Calculating Whether Point Is On A Line With An Equation

If \(\displaystyle f(x)\) is defined as follows, is the point \(\displaystyle \left ( -2,5\right )\)on \(\displaystyle f(x)\)?

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

Possible Answers:

Yes

Cannot be calculated from the provided information

No

f(x) is undefined at (-2,5)

Correct answer:

Yes

Explanation:

To find out if (-2,5) is on f(x), simply plug the point into f(x)

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

Becomes,

\(\displaystyle \small \small 5=4*-2+13=-8+13=5\)

So yes, it does!

Example Question #5 : Calculating Whether Point Is On A Line With An Equation

Which of the following are points along \(\displaystyle g(x)\) if

\(\displaystyle {}g(x)=4x^2-8\).

Possible Answers:

\(\displaystyle (3,28)\)

\(\displaystyle (-3,-28)\)

\(\displaystyle (4,64)\)

\(\displaystyle (3,-28)\)

\(\displaystyle (2,4)\)

Correct answer:

\(\displaystyle (3,28)\)

Explanation:

One way to solve this one is by plugging in each of the answer choices and eliminating any that don't work out. Begin with our original g(x)

\(\displaystyle {}g(x)=4x^2-8\)

If we plug in 3 we get

\(\displaystyle {}g(x)=4(3)^2-8=4(9)-8=36-8=28\)

So our point is (3,28).

 

Example Question #1 : Calculating The Equation Of A Line

What is the equation of a line with slope \(\displaystyle 1\) and a point \(\displaystyle (1,4)\)?

Possible Answers:

\(\displaystyle y=x+4\)

\(\displaystyle y=x+3\)

\(\displaystyle y=x-4\)

\(\displaystyle y=x+1\)

Correct answer:

\(\displaystyle y=x+3\)

Explanation:

Since the slope and a point on the line are given, we can use the point-slope formula:

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

\(\displaystyle m=1\ and\ (1,4)\)

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

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

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

\(\displaystyle y=x+3\)

Example Question #2 : Calculating The Equation Of A Line

What is the equation of a line with slope \(\displaystyle 0\) and point \(\displaystyle (5,2)\)?

Possible Answers:

\(\displaystyle y=x+2\)

\(\displaystyle y=x+5\)

\(\displaystyle y=2\)

\(\displaystyle y=5\)

Correct answer:

\(\displaystyle y=2\)

Explanation:

Since the slope and a point on the line are given, we can use the point-slope formula:

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

\(\displaystyle m=0\ and\ (5,2)\)

\(\displaystyle y-2=0(x-5)\)

\(\displaystyle y-2=0\)

\(\displaystyle y=2\)

Example Question #3 : Calculating The Equation Of A Line

What is the equation of a line with slope \(\displaystyle -\frac{4}{3}\) and a point \(\displaystyle (-8,7)\)?

Possible Answers:

\(\displaystyle y=-\frac{4}{3}x-\frac{3}{11}\)

\(\displaystyle y=\frac{4}{3}x+\frac{11}{3}\)

\(\displaystyle y=-\frac{4}{3}x-\frac{11}{3}\)

\(\displaystyle y=\frac{4}{3}x+\frac{32}{3}\)

Correct answer:

\(\displaystyle y=-\frac{4}{3}x-\frac{11}{3}\)

Explanation:

Since the slope and a point on the line are given, we can use the point-slope formula:

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

slope: \(\displaystyle -\frac{4}{3}\) and point: \(\displaystyle (-8,7)\)

\(\displaystyle y-7=-\frac{4}{3}(x-(-8))\)

\(\displaystyle y-7=-\frac{4}{3}(x+8)\)

\(\displaystyle y-7=-\frac{4}{3}x-\frac{32}{3}\)

\(\displaystyle y=-\frac{4}{3}x-\frac{32}{3}+7\)

\(\displaystyle y=-\frac{4}{3}x-\frac{32}{3}+\frac{21}{3}\)

\(\displaystyle y=-\frac{4}{3}x-\frac{11}{3}\)

Example Question #1 : Calculating The Equation Of A Line

Find the equation of the line through the points \(\displaystyle (4, -2)\) and \(\displaystyle (1, 7)\).

Possible Answers:

\(\displaystyle y=2x+9\)

\(\displaystyle y=-3\)

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

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

\(\displaystyle y=-3x+10\)

Correct answer:

\(\displaystyle y=-3x+10\)

Explanation:

First find the slope of the equation.

m =\frac{rise}{run} =\frac{7 + 2}{1-4} = \frac{9}{-3}=-3\(\displaystyle m =\frac{rise}{run} =\frac{7 + 2}{1-4} = \frac{9}{-3}=-3\)

Now plug in one of the two points to form an equation.  Here we use (4, -2), but either point will produce the same answer.

y-(-2)=-3(x-4)\(\displaystyle y-(-2)=-3(x-4)\)

y + 2=-3x + 12\(\displaystyle y + 2=-3x + 12\)

y=-3x+10\(\displaystyle y=-3x+10\)

Example Question #1 : Calculating The Equation Of A Line

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

Find the equation of \(\displaystyle \overline{JK}\) in the form \(\displaystyle y=mx+b\).

Possible Answers:

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

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

\(\displaystyle \small \small y=\frac{x}{2}+6\)

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

\(\displaystyle \small \small y=2x+3\)

Correct answer:

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

Explanation:

Given that JK passes through (4,5) and (144,75) we can find the slope as follows:

Slope is found via:

\(\displaystyle m=\frac{y'-y}{x'-x}\)

Plug in and calculate:

\(\displaystyle \small \small m=\frac{75-5}{144-4}=\frac{70}{140}=\frac{1}{2}\)

Next, we need to use one of our points and the slope to find our y-intercept. I'll use (4,5).

\(\displaystyle \small 5=\frac{1}{2}*4+b\)

\(\displaystyle \small b=5-2=3\)

So our answer is: 

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

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