The notation [x ] stands for the greatest integer that is less than or equal to x. Calculate [-1,2]

Answer 1

I assume you refer to the floor function, namely ⌊x⌋ represents the greatest integer which is less than or equal to x.

You can figure this out by drawing the given number x on the number line, and the next integer equal to or to the left of the given number is then ⌊x⌋.

For example,
⌊4.5⌋ = 4
⌊3⌋ = 3
⌊-0.4⌋ = -1
⌊-2⌋ = -2
⌊-10.2⌋ = -11

In the case given,
⌊1,2⌋ is not clear, because the floor function takes only one number as the argument, unless the "," is meant to be a decimal symbol, which is current in French speaking countries.
In that case,
⌊-1,2⌋
= ⌊-1.2⌋
= -2