I need help, which classification group does not include triangles

Can someone check if i did this correct. it’s number 4 if you’re wondering.

If f(x) = x+8 and g(x) = 4x- 3, find (f+g)(x)

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.