The learner understands subtraction equations as statements of equality and solves forms such as and with integer or rational-number constants by applying the inverse operation of addition while preserving equality. The reasoning includes distinguishing the variable’s position, interpreting subtraction as adding an additive inverse, and checking a solution by substitution; this scope excludes multi-step equations, variables on both sides, and nonlinear equations.
A subtraction equation is a statement that both sides have the same value. To solve it, use addition to undo subtraction while doing the same thing to both sides.
First notice where the variable is:
Example: Solve
Since is the second number being subtracted, do not simply add . First remove the by adding to both sides:
This simplifies to
Now take the additive inverse of both sides to change into :
Check the solution by substituting for :
The equation is true, so the solution is
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