Answer:
a constant is a data item whose value cannot change during the program execution just as its name implies that the value is constant a variable is a data item whose value can change during the program's execution . Thus as its name implies the the value can vary
Variance of a continuous random variable X is defined as
Standard deviation is defined as

Hence standard deviation is the positive square root of variance.
Y: x-1 that is the answer. I think so.
PYTHOGOROS THEROEM :-
ITS LIKE:- AC² = AB² + BC²