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Expression : An expression is a succession of constants, variables and mathematical operations that if evaluated for specific values of the variables represents a number.
What is the value of the expression $(x+1)(x-1)$ for $x=20?$
Number : A number $x$ is a mathematical symbol representing a quantity.
What is the value of the expression $x$ for $x=-5?$
Constant : Constant is another word for a fixed number that is mainly used in the context of expressions or functions like $f(x)=c$ that are equal to the same number irrespective of any variable.
Independence : Random variables $X,$ $Y$ are called independent if $P[X\in A, Y\in B]=P[X \in A]P[Y \in B].$ Independent identically distributed random variables feature prominently in the law of large numbers and the central limit theorem. Vectors $x_1,x_2\ldots, x_n$ are called linearly independent if $\lambda_1 x_1+\lambda_2 x_2+\ldots+\lambda_n x_n=0$ implies $\lambda_1=\lambda_2=\ldots=\lambda_n=0.$
What is the value of the expression $2$ for $x=1?$