Question 98·200 Super-Hard SAT Math Questions·Algebra
In the given system of equations, is a constant. Which choice gives the value of for which the system has no solution?
For “no solution” linear systems, translate the situation into geometry: two distinct parallel lines. Rewrite each equation so it’s easy to identify the slope (either as or by comparing coefficients). Set the slopes equal to force parallelism, then quickly check that the intercepts (or constants) are not also proportional, which would make the same line instead of no solution.
Hints
Combine like terms first
In each equation, move the -term on the right side to the left side so you can simplify.
Think about what “no solution” means for two lines
A system of two linear equations has no solution when the two lines never intersect.
Compare slopes, not intercepts
After rewriting both equations as , focus on making the slopes match.
Desmos Guide
Enter the two lines in slope-intercept form
In Desmos, enter
When you type the second equation, Desmos will create a slider for .
Create an equation that represents “slopes are equal”
The slopes are and . To find when they match, graph the line
This graph uses as the input value for .
Read the -intercept as the value of
Find the -intercept of . That -value is the that makes the slopes equal.
Then confirm on the original graph that with this , the two lines are parallel (same steepness) and do not overlap (different intercepts).
Step-by-step Explanation
Rewrite each equation in slope-intercept form
First equation:
Second equation:
Use the “no solution” condition (parallel lines)
For no solution, the lines must be parallel, so their slopes must match.
From the first equation, slope is .
From the second equation, slope is .
Set them equal:
Solve for and confirm the lines are distinct
Solve:
The -intercepts are and , which are different, so the lines are distinct and parallel. Therefore, the system has no solution when is
.