Question 98·Medium·Nonlinear Functions
The function is defined by . The graph of is obtained from the graph of by first reflecting it across the -axis and then translating it 2 units to the right. Which equation defines ?
For transformation questions, always work directly with the function rule and apply transformations in the order given. A reflection across the -axis multiplies the entire function by (outside the function), while a horizontal shift of units right replaces with inside the function. Write the intermediate function after each step, simplify carefully, and only then compare the final expression to the answer choices; this avoids mixing up horizontal directions or forgetting how reflections change constants.
Hints
Think about what reflection across the x-axis does
When you reflect a graph across the -axis, how do the -values change? How can you show that change using the function ?
Apply the reflection to the equation
Write a new function that represents the reflection of across the -axis. Start by writing and then substitute .
Now handle the horizontal shift
Once you have the reflected function , a shift 2 units to the right means you should replace with what expression inside ?
Simplify and compare
After you substitute into for the rightward shift, simplify the expression inside the square root and compare your final equation to the answer choices.
Desmos Guide
Enter the original function
Type f(x)=sqrt(x+4)-3 to graph the given function .
Reflect across the x-axis
On a new line, type r(x)=-f(x) to graph the reflection of across the -axis. Observe how the graph flips over the -axis and note the new equation shown by Desmos for .
Translate the reflected graph 2 units to the right
On another line, type g(x)=r(x-2) (or equivalently g(x)=-f(x-2)) to shift the reflected graph 2 units to the right. Look at the equation Desmos displays for g(x) and compare that equation to the answer choices to see which one matches.
Step-by-step Explanation
Interpret the given function and the transformations
The function is
You are told that is obtained from the graph of by:
- Reflecting it across the -axis.
- Then translating (shifting) it 2 units to the right.
We will apply these transformations in this order to the equation of .
Reflect across the x-axis
Reflecting a graph across the -axis changes each -value to its opposite, so algebraically you replace with .
So the reflected function is
Substitute :
This is the equation after reflection but before the horizontal shift.
Translate the reflected graph 2 units to the right
To translate a graph 2 units to the right, you replace with in the function.
We now apply this to the reflected function :
Now simplify the expression inside the square root:
so
This matches answer choice C.