Question 66·Hard·Nonlinear Functions
For , the functions are defined as follows.
I.
II.
Which of these equations displays, as a constant or coefficient, the maximum value of the function it defines, where ?
For SAT questions about exponential functions and maximum/minimum values on a restricted domain, first decide whether the function is increasing or decreasing; for expressions like with , the function decreases as increases, so the maximum on is at . Quickly evaluate the function at the endpoint(s) of the domain to get the extreme values, then carefully reread the question to see what they want you to do with that value—in this case, checking whether it appears explicitly as a constant or coefficient in the function’s formula as written. Staying alert to wording like "displays as" or "as written" helps avoid assuming algebraic rewrites are allowed when they are not directly visible.
Hints
Locate where the maximum can occur
For each function, think about how behaves as gets larger. On the domain , is the function increasing or decreasing? Where would a decreasing function have its maximum on this domain?
Evaluate at the key -value
Once you know where the maximum occurs (based on whether the function increases or decreases), plug that -value into each function to get its maximum value.
Compare the maximum to the written equation
After you find the maximum value of each function, look back at the equation as written. Does that number appear directly as a standalone constant or as a coefficient multiplying something, without doing any extra algebra?
Pay attention to how the expression is written
For function I, notice that the number is inside the exponent on . For function II, notice there is a number in front of . Which presentation more clearly shows the maximum value as a coefficient?
Desmos Guide
Graph both functions
In Desmos, enter the two equations on separate lines:
y = 4^(-(x+1))y = (1/4)*4^(-x)You will see two decreasing exponential curves.
Focus on the domain x ≥ 0 and find the maximums
To see only , you can restrict each function, for example:
y = 4^(-(x+1)) {x>=0}y = (1/4)*4^(-x) {x>=0}Then, click each graph near to see the coordinate of the point where . The -value there is the maximum for that function on .
Compare those maximum values to the equations
Note the -value you see at for each graph. Then look back at each equation and check whether that -value is written directly as a standalone number or coefficient in the formula. Decide which function(s) meet this condition.
Step-by-step Explanation
Understand what the question is really asking
The question is not only about finding the maximum value of each function; it is asking whether that maximum value appears directly as a constant or coefficient in the equation as written.
So for each function:
- First: Find its maximum value when .
- Second: Check if that number is actually written somewhere in the formula as a constant (like a standalone number) or as a coefficient (a number multiplying something).
Find where the maximum occurs for each function
Both functions are exponential decay functions because they involve raised to a negative exponent.
- As increases, gets smaller.
- For , this means each function is decreasing as increases.
If a function is decreasing on , its largest value in that domain happens at the smallest , which is .
So for both functions, the maximum value occurs at .{
Compute the maximum value of each function
Now plug in to each function.
For I: .
- .
For II: .
- .
So both functions have the same maximum value on .{
Check whether each equation shows that maximum as a constant or coefficient
Now compare the maximum value with the way each equation is written.
-
Function I: .
- The constants you see are , (from the negative sign), and in the exponent.
- The number is not written as a separate constant or coefficient; it only appears after simplifying when we plug in .
- So the equation for I does not display the maximum value as a constant or coefficient.
-
Function II: .
- The coefficient in front is .
- The maximum value we found is also .
- Here, the maximum value is exactly the coefficient in the equation.
Therefore, only function II displays its maximum value as a constant or coefficient. So the correct answer is II only.