Question 114·Hard·Equivalent Expressions
Which of the following expressions is (are) a factor of ?
I.
II.
For questions asking which binomials are factors of a polynomial, use the Factor Theorem instead of doing full polynomial division. For each binomial, first find the value of that makes it zero (for , solve ; for , use ), then plug that value into the polynomial. If the result is 0, the binomial is a factor; if not, it is not a factor. Test each option quickly and then match which ones work to the answer choices.
Hints
Connect factors to zeros
If a binomial like is a factor of a polynomial, what happens when you plug in into the polynomial?
Handle the binomial
Solve to find the -value to test in the polynomial. When you plug that value in, carefully simplify step by step.
Handle the binomial
For , what value of makes it zero? Plug that into the polynomial and see if the result is 0.
Compare your results
After testing each candidate binomial, decide for each one separately whether it is a factor, then match that to the answer choices (I only, II only, both, or neither).
Desmos Guide
Enter the polynomial
Type f(x) = 4x^3 - 12x^2 - 7x + 30 into Desmos to define the polynomial.
Test I:
Solve to get the test value . In Desmos, type f(-1.5) and check the output; if it is 0, then is a factor.
Test II:
For , the test value is . In Desmos, type f(2) and check the output; if it is 0, then is a factor.
Match to the answer choices
Based on what Desmos shows for f(-1.5) and f(2), decide for each binomial whether it is a factor (output 0) or not (nonzero), then pick the answer choice that matches which of I and II are factors.
Step-by-step Explanation
Use the Factor Theorem idea
A quick way to test if a binomial is a factor of a polynomial is:
- If the binomial is , plug in .
- If the result is 0, then is a factor of the polynomial.
For a binomial like , first solve to find the -value to plug in.
Test I: Check whether is a factor
First, find the -value that makes :
- .
Now plug into the polynomial :
- , so .
- , so .
- .
Combine the terms:
- .
- First combine the fraction terms: .
- Now combine everything: .
Since plugging in gives 0, is a factor of the polynomial.
Test II: Check whether is a factor
For , the zero is .
Plug into the polynomial :
- .
- .
- .
Now add all terms:
- .
- Combine: .
Since plugging in gives 0, is also a factor of the polynomial.
Decide which statements are correct
We tested both binomials using their zeros:
- For I (), plugging in made the polynomial equal 0, so I is a factor.
- For II (), plugging in also made the polynomial equal 0, so II is a factor.
Therefore, both I and II are factors of , so the correct answer is I and II.