Question 94·Easy·Linear Equations in Two Variables
What is the equation of the line that passes through the points and in the -plane?
For line-through-two-points questions, quickly compute the slope with , paying close attention to signs and whether the slope should be positive or negative based on how the points move. Then plug the slope into and use one of the points to solve for . Finally, write the full equation and either match it to the answer choices or quickly test each choice by substituting the given points to see which equation both points satisfy.
Hints
Start with the slope
Use the slope formula with the points and . Be careful with the minus signs.
Think about the sign of the slope
As increases from to , does increase or decrease? Should the slope be positive or negative based on how the points move?
Use slope-intercept form
Once you know the slope , write the equation as and plug in one of the points to solve for .
Check your equation
After you find an equation, plug in both and to make sure they satisfy it. Only one answer choice will work for both points.
Desmos Guide
Plot the given points
In Desmos, type (-2, -3) and (4, 0) on separate lines to plot the two points. You should see them appear on the graph.
Graph answer choice A
Type y = -1/2 x - 2 into Desmos. Check whether this line goes exactly through both plotted points and . If it misses either point, this choice is not correct.
Graph answer choice B
Type y = 1/2 x + 2. Again, check whether the line passes through both plotted points. If it does not pass through both, eliminate this option.
Graph answer choice C
Type y = 1/2 x - 2. See whether this line goes through both and . If it does, note that this equation is a candidate for the correct answer.
Graph answer choice D
Type y = -1/2 x + 2. Check whether this line passes through both given points. After testing all four, identify which line contains both points; that equation is the correct choice.
Step-by-step Explanation
Find the slope of the line
Use the slope formula for two points and :
Let and :
So the slope of the line is positive and equals . This immediately tells you the correct equation must have a positive slope.
Write the general slope-intercept form with the found slope
A line with slope can be written in slope-intercept form as
You already found , so substitute that into the equation:
Now you just need to find the value of , the -intercept.
Use one of the points to solve for the y-intercept
The line passes through both given points, so each point must satisfy .
Use the point and substitute and :
Solve for :
So the -intercept of the line is .
Write the final equation and match it to an answer choice
Now substitute back into the equation :
This matches answer choice C) , which is the equation of the line through and .