Question 86·Medium·Linear Equations in One Variable
In the linear equation , is a constant. For which value of does the equation have no solution?
For questions asking when a linear equation in one variable has no solution (or infinitely many), first simplify the equation so all -terms are on one side and constants on the other, giving something like where and depend on a parameter. Then use the rule: if there is one solution, if and there are infinitely many solutions, and if and there is no solution. Apply these conditions directly to find the parameter value instead of testing every answer choice by hand.
Hints
Simplify the equation first
Rewrite by moving all -terms to one side and all constant terms to the other side. What do you get?
Recognize the structure of the simplified equation
After simplifying, your equation should look like , where and each involve . Think about what values of and make such an equation have no solution.
Focus on when x disappears
A linear equation in has no solution when the term cancels out (coefficient becomes 0) but the remaining statement is false (a nonzero constant equals 0). For which value(s) of does the coefficient of become 0, and what happens to the constant term then?
Desmos Guide
Set up the two sides as functions for a chosen c
For each answer choice, replace with that value and enter the left and right sides as two separate functions in Desmos, for example for a given :
- (With replaced by the specific number you are testing.)
Check intersections to determine the number of solutions
For each tested value of , look at the graphs of and :
- If the lines intersect at exactly one point, the equation has one solution.
- If the lines overlap completely (same line), there are infinitely many solutions.
- If the lines are parallel but distinct (same slope, different intercepts), there is no solution. Identify which choice for makes the two lines parallel and distinct; that is the correct answer.
Step-by-step Explanation
Collect all x-terms on one side
Start with the given equation:
Subtract from both sides and subtract from both sides to group -terms and constants:
Simplify the left side:
Think about when a linear equation has no solution
The simplified equation is:
For a linear equation of the form :
- If , there is exactly one solution .
- If and , there are infinitely many solutions (every works).
- If and , there is no solution (you get a false statement like ).
Here, and . We want the no solution case.
Set up the conditions for no solution
For no solution, we need:
- The coefficient of to be :
- The constant term to not be :
These two conditions together will give the value of that makes the equation have no solution.
Solve the conditions and identify the correct choice
First solve the coefficient condition:
Now check the constant term with this value:
So when , the equation becomes , which is impossible and has no solution. Thus, the correct answer is (choice C).