Which ones are linear and not linear? a, b, c, and d

What is the inverse of the function f(x) = 2x + 1?

X2 + y 2 = 36 x + y = 6 solve the system of equations.

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.