\[1)\ \sqrt{- 100} = \sqrt{100} \bullet \sqrt{- 1} = 10i;\]
\[2)\ \sqrt{- 0,25} = \sqrt{0,25} \bullet \sqrt{- 1} = 0,5i;\]
\[3)\ \sqrt{- 12} = \sqrt{4} \bullet \sqrt{3} \bullet \sqrt{- 1} = 2\sqrt{3}i;\]
\[4)\ \sqrt{- 27} = \sqrt{9} \bullet \sqrt{3} \bullet \sqrt{- 1} = 3\sqrt{3}i.\]