Question 51·Hard·Linear Equations in One Variable
How many real solutions does the equation
have?
For rational equations like this, first note any values that make denominators zero and exclude them. Then simplify each side by factoring and canceling common factors where allowed. Once simplified, rewrite the equation in a basic form and solve; if you get an impossible statement (like a nonzero fraction equal to 0 or ), conclude there are no solutions. Always check that any potential solutions are in the domain and do not make a denominator zero.
Hints
Start with the denominators
Both sides of the equation have a denominator of . What value of must be excluded so the denominators are not zero?
Simplify one side first
On the left side, try factoring . Can you cancel anything with the denominator ?
Compare the two sides after simplifying
After simplifying the left side, rewrite the equation. What happens if you subtract 4 from both sides? What kind of equation do you get for the remaining fraction?
Think about when a fraction equals zero
For a fraction of the form , under what condition does it equal 0? Does ever meet that condition for any real ?
Desmos Guide
Graph both sides as separate functions
In Desmos, enter the left side as y = (4x + 12)/(x + 3) and the right side as y = 4 + 2/(x + 3). Make sure both graphs are turned on.
Look for intersection points
Visually inspect the graph and, if needed, zoom in and out. Use the tap/click feature on Desmos to find any intersection points between the two curves. The -coordinates of intersection points (excluding , where there is a vertical asymptote) are the real solutions to the equation.
Step-by-step Explanation
Identify domain restrictions
Both denominators are , so cannot make a denominator zero.
Set the denominator not equal to zero:
Any solution we find must satisfy .
Simplify the left-hand side
Look at the left-hand side:
Factor the numerator:
So
for all such that (we already excluded ).
Rewrite the equation using the simplification
Using the simplification from Step 2, the original equation becomes
Subtract 4 from both sides:
Now think about what this means: a fraction has numerator 2 and denominator .
Check if the resulting equation can ever be true
For to equal 0, its numerator would have to be 0. But the numerator here is 2, which is never 0, no matter what real value has.
So has no real solution, and was already excluded because it makes the denominators zero.
Therefore, the original equation has zero real solutions, which corresponds to choice D.