The sqrt of a negative number is the same just add i to it. So the √-49 is just i ×√49, or 7i. To solve the second, just do it normally knowing what I just told you.
x²+4=0
x²=-4
√x²=plus or minus √-4
x=plus or minus 2i
I don't have the plus or minus symbol so I just wrote it out.
