In order for an expression to be an equation, it must have an equal sign a variable more than one variable an addition sign

In order for an expression to be an equation, it must have  an equal sign.

Equation is a expression in which one quantity is equal to the other.

It denoted by a equality sign (=)

For example if we write a=b then it means that both a and b are equal.

Also , the sign < or > shows the strict inequality and the sign ≤ or ≥ denote the inequality with an equality sign i.e. it is not a strict inequality.

Hence, the inequality of the type:

           x+y<6

is called a linear inequality.

and expression of the type:

  x+2y=7 is called a linear equation.

        Hence, the answer is:

         an equal sign

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