Which of the following is a zero of the function f(x) = x3 - x2 - 21x + 45.
A. -3
B. 1
C. 3
D. 5

Question

Which of the following is a zero of the function f(x) = x3 - x2 - 21x + 45.
	A.	-3
	B.	1
	C.	3
	D.	5

anonymous · Answer

If a number is a zero of a function, then when you evaluate the function at that number, the answer will be zero.
So ONE way to solve this problem is to plug in each of those four answer options (one at a time) back into the function and see which one equals zero.

For example, to check answer option A:
$$f(-3)=(-3)^{3} - (-3) ^{2} - 21(-3) + 45$$
Then evaluate that and see if it equals zero.  If it does, that's your answer.  If it doesn't, try another answer option.

anonymous · Answer

i got c is that correct?

anonymous · Answer

That's what I got too! :)  Good job!