Question 35·Medium·Linear Equations in One Variable
In the equation above, is a constant. For what value of does the equation have no solution?
(Express the answer as an integer)
For this type of problem, treat the variable (here, x) normally and the letter like k as a constant you are solving for. First, simplify the equation and rearrange it into the form (expression in k)·x = (another expression in k). Then use the rules for linear equations: if the coefficient of x is nonzero, there is one solution; if both the coefficient and constant are zero, there are infinitely many solutions; and if the coefficient is zero but the constant is nonzero, there is no solution. Set the coefficient of x equal to zero, check that the constant is not zero for that k, and that k is your answer.
Hints
Start by simplifying the left side
Try distributing across the parentheses on the left side so that there are no parentheses in the equation.
Group like terms
After distributing, move all the x terms to one side of the equation and the constant terms (without x) to the other side.
Think about when a linear equation has no solution
If you end up with something like , what has to be true about and so that there is no value of that makes the equation true?
Apply that idea to this equation
Identify the expression that plays the role of (the coefficient of ) and the expression that plays the role of (the constant), and use the no-solution condition on them to find .
Desmos Guide
Graph both sides as functions
In Desmos, type y = k(3x - 2) on one line and y = 3x + 5 on another line. Desmos will automatically create a slider for k.
Use the slider to explore different k values
Move the k slider and watch how the graph of y = k(3x - 2) changes compared with y = 3x + 5. You are looking for the k value where the two lines have the same slope (are parallel) but never intersect.
Read off the needed k value
Stop when the two graphs are parallel and do not touch at any point. The current value shown for k on the slider is the value that makes the equation have no solution.
Step-by-step Explanation
Distribute k on the left side
Start by expanding the left-hand side of the equation.
Distribute :
Collect x-terms together
Get all the x terms on one side and the constants on the other.
Subtract from both sides:
Factor out from the first two terms:
Add to both sides:
Use the condition for "no solution" to find k
Now the equation looks like .
For an equation of the form :
- If , there is exactly one solution for .
- If and , there are infinitely many solutions.
- If and , there is no solution.
Here, and . For no solution, we need and .
Solve :
k = 1