Algebra

Remember     sqrt (-1) = i  ?

3 + sqrt (-16)   = 

3 + sqrt (16*(-1) )   =   3 + 4i      

      and   6-sqrt(-64) = 6 - 8i          take it from here ............

Square roots of negative numbers will have "i"  in them. \(\sqrt{-1}=i\). So the square root of a negative number would be the square root of the number if it were postiive with an i.