Question 3·Hard·Nonlinear Functions
The function is given.
What is the minimum value of the function?
(Express the answer as an integer)
For quadratic minimum/maximum questions on the SAT, first check the coefficient of : if it’s positive, the vertex gives a minimum; if negative, it gives a maximum. Use the vertex formula to quickly find the x-coordinate, then plug that value back into the function to get the corresponding y-value. Work carefully with arithmetic signs, and remember the question often asks for the function’s value (y), not the x-coordinate where it occurs.
Hints
Think about the shape of the graph
The function is a quadratic. What does its graph look like, and where does a quadratic reach its minimum or maximum?
Use the vertex formula
For a quadratic , the x-coordinate of the vertex is given by . Identify and in this function and compute that x-value.
Find the function value at the vertex
Once you know the x-coordinate of the vertex, substitute that x-value back into and simplify carefully. That result is the minimum value of the function.
Desmos Guide
Graph the quadratic
In Desmos, type y = x^2 - 48x + 2304 to graph the function.
Locate the vertex (minimum point)
Zoom or pan until you can clearly see the lowest point of the parabola. Tap or click on that lowest point (the vertex); Desmos will display its coordinates .
Read the minimum value
Look at the y-coordinate of the vertex shown by Desmos. That y-value is the minimum value of the function .
Step-by-step Explanation
Recognize the type of function and what is being asked
The function is a quadratic of the form with , so its graph is a parabola that opens upward.
For an upward-opening parabola, the minimum value of the function occurs at its vertex. So we need to find the vertex and then find the function value there.
Find the x-coordinate of the vertex
For a quadratic , the x-coordinate of the vertex is given by
Here, and , so
So the vertex occurs at .
Evaluate the function at the vertex to get the minimum value
Now plug into to find the minimum value:
Since the parabola opens upward, this value is the minimum value of the function, which is 1728.