Which of the following is equal too a) 2 b) -2 c) 2i d) 2

You can't have a negative number under a radical that has an even index.  We have an even index since we are dealing with the square root.  Because of that we have to get the imaginary i involved.  .  Keeping that in mind, let's rewrite our problem: .  If -1 equals i-squared, we can sub that in.  Also, since 8 = 4*2 and 4 is a perfect square, let's break that down at the same time: .  i-squared is a perfect square which can be pulled out as a single i, and 4 is a perfect square which can be pulled out as a 2.  We will leave a 2 under the radical.  Here's your simplification: , choice C from above.