Question 89·Medium·Linear Functions
Line is defined by the equation . Line is parallel to line and passes through the point .
Which of the following is an equation of line ?
For parallel-line questions, immediately convert the given line to slope-intercept form to read off the slope. Use that same slope for the new line, plug the given point into to solve quickly for , and then match your final equation to the answer choices, optionally checking by substituting the point to confirm it lies on that line.
Hints
Find the slope of line k
First, rewrite in the form so you can easily see the slope of line .
Use the property of parallel lines
Parallel lines have the same slope. Once you know the slope of line , use that same slope for line .
Use the point on line m
After you write line as with the correct slope, plug in and to find .
Check which option fits
Once you find the full equation of line , compare it to the answer choices and also make sure it passes through .
Desmos Guide
Graph line k to see its slope
Type 4y - 8x = 12 into Desmos. Then, if needed, click the graph or rewrite it as y = 2x + 3 so you can recognize that the slope of line is .
Graph each answer choice
Enter each option into Desmos as separate equations: y = -2x - 17, y = 2x + 17, y = -2x + 17, and y = 2x - 17. Visually compare their steepness and direction to line to see which have the same slope (are parallel).
Plot the given point and test lines
Plot the point (6, -5) in Desmos. Then look at which of the lines that are parallel to line also pass exactly through the point (6, -5). The line that is both parallel and passes through the point is the correct answer.
Step-by-step Explanation
Rewrite line k to find its slope
Start with the equation of line :
Solve for to put it in slope-intercept form :
Divide every term by :
So line has slope .
Use the fact that parallel lines have the same slope
Parallel lines have equal slopes.
Since line has slope , line must also have slope .
So line has the form
for some (the -intercept) that we still need to find.
Plug in the given point to find the y-intercept
We know line passes through , so its equation must be true when and .
Substitute and into :
-5 = 12 + b
Solve for b and match with an answer choice
From the equation
subtract from both sides:
b = -17
y = 2x - 17