What is the end behavior of the graph of the polynomial function y = 7x12 – 3x8 – 9x4?

To know the end behavior of the graph, we look at the degree of the polynomial and the sign of the coefficient of the highest exponent variable.
The degree is 12, which is even.
The coefficient is 7, which is positive.

Therefore, for this type of polynomial function, the end behavior is:
f(x)--> +∞, as x--> −∞
f(x)--> +∞, as x--?>+∞