All numbers have two square roots. The principle positive square root as well as the negative square root. The reason for this is because when multiplying a negative number by another negative number we get a positive result. So for example:
8*8 = 64
but. . .
-8*-8 also = 64
So the square root of 64 is both positive 8 and negative 8
The first few should be obvious:
√64 = ± 8
√169 = ± 13
√256 = ± 16
√400 = ± 20
√1600 = ± 40
For the next you need to break apart the decimals and think of them as fractions:
√0.04 = √(4/100) = √4 / √100 = ± 2/10 = ± 0.2
√0.36 = √36/100 = ± 6/10 = ± 0.6
√1.21 = √121/100 = ± 11/10 = ± 1.1