# Checking for careless mistakes using the Substitution Method

- Normal method of checking (i.e. check your working from front to back again),
**may or may not find the error** - Using
**Substitution Method of checking****guarantees that your answer is correct**, and will find an error if there is one. - Use
**Substitution Method of checking**for all**algebra/solving/simplify**questions worth**2 marks or more.**You will be able to**save many many marks**using this method! **Only takes 10 seconds**with practice. (use calculator)

### Example (using substitution method)

Express as a single fraction in its simplest form. [2 marks]

After getting your answer (), you can substitute in the value .

When, , , and

Since both expressions give the same value, you have just checked that your answer is correct!