KomFi's dominant technique on any 'which expression is equivalent' item: pick a convenient x (1 or 2, avoiding values that zero a denominator), evaluate the original and every option, and take the match. It is immune to factoring and sign errors, faster than the algebra on every item of this type, and uniquely it detects when nothing matches — meaning you misread the problem. A technique that detects your own errors outranks one that merely produces answers.