I have a question:
are all polynomial function has y-intercept and x-intercept?
It is not linear, it is quadratic. Are you aware of the differences?
My function has a y-intercept, you can find it by making $\displaystyle x=0$
$\displaystyle g(x) = -x^4-5$
has order $\displaystyle > 3$ and no x-intercpets
The y-intercept is where x= 0. Since evaluating a polynomial involves only multiplication and addition or subtraction, which are possible for any real number, the domain of a polynomial always includes all real numbers, including 0.
The x-intercept is where y, the value of the polynomial, is 0. Any polynomial of odd degree crosses the x-axis and so has an x-intercept. Polynomials of even degree may or may not have an x-intercept.