4.4.45
for the following polynomial, one zero
is given. find the remaining zeros.
the
(sim
to se!
p(x) = x4 + 27x^2 - 324, 6i is a zero.

Step-by-step explanation:

If 6i is a zero then -6i is a zero.

In general, if a+bi is a zero then a-bi is a zero (if the polynomial has real coefficients which this one does: 1,27,-324).

Let's test it to see:

Check

Check

So yep they both give us 0 when we plug it in.

If x=6i is a zero then x-6i is a factor by factor theorem.

If x=-6i is a zero then x+6i is a factor by factor theorem.

What is (x-6i)(x+6i)?

Let's use the multiply conjugates formula: .

Now we know is a factor of .

We can use long division or we could try to find two numbers that multiply to be -324 and add up to be 27 since this is a quadratic in terms of with leading coefficient of 1.

Well we already know we are looking for number times 36 that would give us -324.

So -324=-9(36) and 27=-9+36

So the factored form in terms of real numbers is:

We already know the first factor can be factored as (x+6i)(x-6i).

The other can factored as (x-3)(x+3) since (-3)(3)=-9 and -3+3=0.

So the complete factored form is

.