General

Rage at math teacher

I am so angry at my online math teacher right now. In the beginning of the year, she graded my assignment totally incorrect (I got everything correct and she gave me a 50%). Now in the second semester of the course, she just gave me this problem:
Determine the zeros of f(x) = x^4 - x^3 + 7x^2 - 9^x - 18. (1 point)

Using complete sentences, describe how you would verify the zeros of a function. Use your description to verify one of the problems submitted for the assessment. (2 points)

I used the first question. My answer was:

x=-1; x=2; x=3i; x=-3i
To verify the zeroes of a function, set each of the solutions equal to x. Put the additive inverse of the solution on the same side of the equation as x so that x+k=0. Using the zero property, since at least one of the factors of an equation that equals zero must be equal to zero, you can multiply each equation together. You get (x+k1)(x+k2)(x+k3)(x+kn)... where n is the number of solutions. Multiply the expression out to get the side of the function equivalent to f(x).
To use this method to check the answer on number 3,
x=-1;x=2;x=3i;x=-3i
(x+1)(x-2)(x-3i)(x+3i)
(x²-x-2)(x²+9)
x^4-x^3+7x^2-9x-18.

I get it back graded, I get both parts of this question incorrect: my explanation and the work after are each a part;

She says: Nice job solving polynomial equations I need you to put #7 in your own words and show how this is done.. your example doesn't show how you are checking that the zeros are indeed the correct zeros.
Hope that helps!
me: I understand how it doesn't show the work, but it was completely in my own words. The lesson doesn't even use coherent sentences; it just gives examples.

There are several similar cases like this. I don't want to withdraw from the course, but these are really lowering my grade (3 percentage points by my calculations).

Anyone else have a similar experience and can offer advice?
(Edited to make it slightly more readable, and to fix exponents)