Question 18·Hard·Nonlinear Functions
The table below gives selected values of a polynomial function .
Based on the values in the table, which of the following must be a factor of ?
For polynomial questions using a table of values, immediately scan the table for any -values where —these are guaranteed zeros. Use the Factor Theorem to convert each zero into a linear factor , and if needed, combine them into a product to include multiple zeros. Then compare the implied zeros of each answer choice with the ones from the table: correct answers must match all known zeros and not contradict any given values. Pay close attention to words like "must" or "could" so you only choose factors that are certain from the data, not merely possible.
Hints
Look for zeros in the table
Which -values in the table make equal to ? Those -values are the zeros (roots) of the polynomial.
Connect zeros to factors
For a polynomial, what factor do you get if you know that ? Think about an expression like and how it behaves when .
Combine the information
Once you know all the -values from the table where , ask: which answer choice represents factors that would give exactly those zeros?
Check consistency with the table
For any choice that includes a factor , that would force . Compare each candidate's implied zeros with the values in the table to see which one must be true.
Desmos Guide
Enter the data points from the table
In Desmos, add a new table (using the "+" button, then "Table"). In the first column (for ), enter , , , , and . In the second column (for ), enter , , , , and respectively so you have the points , , , , and plotted.
Identify the zeros from the graph of points
Look at the plotted points and find which ones lie on the -axis (where the -value is ). The -coordinates of those points are the zeros of , which correspond to linear factors of the form .
Match zeros to factor choices
Using the zeros you observed, think about which answer choice has factors that would produce exactly those zeros (via expressions of the form ). Pick the choice whose factors align with the -coordinates of the points lying on the -axis in your Desmos plot.
Step-by-step Explanation
Find where the polynomial equals zero
Look at the column in the table and identify which -values give .
From the table:
So and are zeros (roots) of the polynomial .
Recall the Factor Theorem
For any polynomial , the Factor Theorem says:
- If , then is a factor of .
- Equivalently, each zero of gives a linear factor .
So each zero you found in the table corresponds to a linear factor of .
Express the factors in general form
Let the two zeros be and .
By the Factor Theorem, the polynomial has linear factors and .
A factor of that has both zeros built in is the product of these two linear factors, .
Now you just need to substitute the actual values of and and compare with the answer choices.
Substitute the zeros and match the answer choice
We have and .
- The factor from is .
- The factor from is .
Combining both zeros into one factor gives .
Among the answer choices, this matches choice D, so must be a factor of based on the table.