What are the 3 methods used for solving a system of equations? which method do you prefer? why?

The 3 methods used in solving a system of equations is : substitution, elimination, and matrices. 

which method do I preferdepends on the equations. 
if they are : x + y = 2and x - y = 4then I prefer elimination... because u can just add them eliminating the y.

but if it is like : y = 2x and x + y = 4then I prefer substitution.

I am not good at matrices...so I dont usually use thembut I believe they are pretty similar to elimination...and shorter. Elimination takes many steps and if u mess up on a beginning step, it carries through to the end.

Ithink the answer is c

Hello! i hope this
since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.