Can someone simplify the square root of -128?

Answer 1

-1281/2 = -11/2 * 1281/2 = i * 1281/2 = i * 641/2 * 21/2 = i * 8 * 21/2

Short of now calculating the value and writing this as a multiple of i this is as simplified as it can be.

The square root of -128 = 8i * 21/2

(note: x1/2 means "the square root of x").