GMAT Math : Calculating whether point is on a line with an equation

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #61 : Coordinate Geometry

Solve for \displaystyle y in the coordinate \displaystyle (3,y) on line \displaystyle 5x+2y=13?

Possible Answers:

\displaystyle -1

\displaystyle 1

\displaystyle -2

\displaystyle 2

Correct answer:

\displaystyle -1

Explanation:

 

To solve for \displaystyle y for \displaystyle x=3, we have to plug \displaystyle 3 into the \displaystyle x variable of the equation and solve for \displaystyle y:

\displaystyle 5(3)+2y=13

\displaystyle 15+2y=13

\displaystyle 2y=13-15

\displaystyle 2y=-2

\displaystyle y=-1

Example Question #61 : Lines

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

Possible Answers:

\displaystyle -1

\displaystyle \frac{1}{2}

\displaystyle 2

\displaystyle 1

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).

 

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