What is seven over twenty one take away one over twenty one in its simplest form

When using the linear combination metho e linear combination method to solve a system of linear equations, the four options are:

What numbers are included in the set of integers? what numbers are not included?

Which of the expressions (on the photo document i inserted) together represent all solutions to the following equation? 8cos(12x)+4=-4 *the answer should be in degrees.* > i would like for someone to explain the process to find the solutions for this.