Question 86·Medium·Linear Equations in Two Variables
In the -plane, line passes through the points and . Which equation represents line ?
When a question asks for the equation of a line through two points, first compute the slope carefully using , watching your signs. Then write and plug in one of the points to find . Finally, either write the full equation and match it to the choice with the same slope and intercept, or quickly eliminate options whose slopes don’t match your computed slope; if needed, plug a point into the remaining choices to see which one works.
Hints
Start by finding the slope
Use the two points and to find the slope with the formula . Be careful with the signs in the numerator and denominator.
Use slope-intercept form
Once you know the slope , write the line as and plug in one of the given points to solve for , the -intercept.
Check both points
After you find an equation, plug in the other point to confirm it lies on the line. The correct equation must work for both given points.
Desmos Guide
Plot the two given points
In Desmos, type (-3, 2) and (5, -2) on separate lines to plot the two points that the correct line must pass through.
Graph each answer choice
On new lines, enter each option exactly as written: y = 2x - 4, y = -1/2 x + 1/2, y = -1/2 x - 1/2, and y = 1/2 x + 1/2. Four lines will appear on the graph.
Identify the matching line
Look at which of the four lines passes through both plotted points and . The equation of that line is the correct answer choice.
Step-by-step Explanation
Find the slope of the line through the two points
Use the slope formula for two points and :
Let be and be :
So the slope of line is .
Write the line in slope-intercept form
Slope-intercept form is , where is the slope and is the -intercept.
We already know , so the equation must look like
Now we just need to find .
Use one point to solve for the y-intercept
Substitute one of the given points into to find . Use :
So:
Compute , so:
Subtract from both sides:
So the -intercept is .
Match to the correct answer choice
From the previous steps, the line has slope and -intercept , so its equation is
Among the answer choices, this matches choice B.