is saying i've been blocked when all I did was copy and paste this: Which equations support the fact that rational numbers are closed under addition?

Select each correct answer.

13+13=23

6√+(−6√)=0

2√+2√=22√

9√+9√=29√

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.