SL 1.6—Deductive proof

Write a deductive proof as linked equalities.

A proof starts from a known expression and uses justified equalities until it reaches the target; each line preserves truth.

Worked example
To show (n+1)²−n²=2n+1, expand to n²+2n+1−n², then simplify.

Worked example
Which line needs justification? every transformation, such as expansion or cancellation, must preserve equality.

Common boundary
A few confirming examples do not prove a statement for all allowed values.