Mathematical convention. There are standard rules of writing expressions and equations. The students must understand and obey these rules, and the teacher must follow them when writing on the board. One rule is that the variable appears to the left of numbers in expressions, and higher powers to the left of lower powers. A second rule is that the isolated variable in an equation must be on the left.

 

As an example of the first rule, the expression 4 – 3x must be written as -3x + 4. The negative sign in front of the x is not justification for writing it last.

 

As an example of the second rule,

 

-3x + 4 = y

 

must be written as

 

y = -3x + 4.

 

SEE THE BOOK FOR MORE DETAILS.