Question 32·200 Super-Hard SAT Math Questions·Algebra
For any real number , which choice gives a point that lies on the graph of both equations?
First check whether the two linear equations are multiples of each other; if they are, they represent the same line, which simplifies the problem. Then test each proposed point by substituting its and into one equation and simplifying: the correct parametric point must make the equation true for every real , meaning the terms cancel and the correct constant remains.
Hints
Compare the two equations
See if one equation can be turned into the other by multiplying both sides by the same nonzero number.
Use just one equation
If the equations represent the same line, you only need to check whether a point satisfies .
Substitute and simplify
Plug the given and into . A point works for any real only if the expression simplifies to with the terms canceling out.
Desmos Guide
Graph the line (either equation)
Enter the equation . Then enter and confirm it graphs as the same line (the graphs overlap).
Create a slider for
Type r=0 and press Enter to create a slider for .
Test each option as a moving point
For each answer choice, enter its point as an ordered pair using (for example, one candidate might look like (3r+2,(15r+11)/7)). As you move the slider, watch whether the point stays on the line.
Choose the point that always stays on the line
The correct choice is the one whose point remains on the line for all values of you test (try several values, including negative and positive).
Step-by-step Explanation
Recognize the relationship between the equations
Multiply the first equation by :
This matches the second equation, so both equations describe the same line.
Reduce the task
Because the graphs are the same line, a point lies on the graph of both equations exactly when it satisfies just one of them (for example, ).
Test each choice by substitution
For each choice, substitute its - and -expressions into and simplify. The correct choice will simplify to without needing a specific value of (the terms should cancel).
Verify the correct point
Substitute and into :
So this point satisfies the first equation for every real , and therefore it lies on the graph of both equations: .