Question 35·Medium·Nonlinear Functions
The function is defined for all real numbers by an equation of the form
where is a constant. If the point lies on the graph of , which of the following equations could represent ?
For function-parameter questions like this, always start from the given general form and plug in the coordinates of the given point to form an equation in the unknown parameter (here, k). Solve that simple equation, rewrite the full function with the found parameter, and then match it to the answer choices—also using any fixed pieces of the form (like a constant +4) to quickly eliminate options that cannot work.
Hints
Use the fact that the point lies on the graph
If the point lies on the graph of , what are the input and output values for the function? How can you substitute these into ?
Set up an equation for k
Plug and into to create an equation with one unknown, .
Solve the equation step by step
After substituting, simplify , then isolate by subtracting 4 from both sides and dividing by the coefficient in front of . Once you have , rewrite and look for that equation among the choices.
Desmos Guide
Graph the general form with a slider
In Desmos, type h(x)=k*(0.5)^x+4. When prompted, make k a slider so you can adjust its value.
Use the point condition to find k
Add a point by typing (2,6); it will appear on the graph. Adjust the slider for k until the curve of passes exactly through the point . Note the value of k at that moment.
Match to the answer choice
Once you know the value of k from Desmos, rewrite the function in the form , then select the answer choice whose coefficient on and constant term match your function.
Step-by-step Explanation
Use the given form of the function
We are told that h has the form , where is a constant. This means the last term must be in the correct answer, and only the coefficient in front of can change.
Substitute the given point into the formula
The point lies on the graph of , which means when , .
So plug and into :
Solve for the constant k
First simplify :
So the equation becomes
Subtract 4 from both sides:
Now divide both sides by to solve for :
Write the function and match it to an answer choice
Compute , so .
Substitute back into the general form to get
Comparing with the choices, this matches option C.