The key identity is (a+b)(a-b)=a²-b². When a numerator contains a radical term, its conjugate changes the sign between the paired terms, so their product removes the cross terms and leaves a rational difference of squares. This algebraic cancellation is why the technique can simplify the radical portion without changing the expression’s value.
Choosing the correct conjugate depends on the numerator’s two-term pattern. For an expression such as a+b, use a-b; if the signs are reversed, use the corresponding sign change. The goal is not merely to introduce another radical, but to create a product governed by the difference-of-squares identity.
Multiplying both numerator and denominator by the same conjugate preserves equivalence because the expression is multiplied by a form of 1. The denominator is essential: changing only the numerator would alter the value. After expansion, the conjugate product supplies a rational factor while the remaining factors can be simplified.
Begin by identifying the radical expression in the numerator and writing its conjugate. Multiply both numerator and denominator by that conjugate, expand the products, apply the difference-of-squares identity, and simplify common factors or constants. Keeping the numerator and denominator grouped during expansion helps preserve the original fraction and makes each algebraic change visible.
Factoring and equivalent forms help determine whether the new expression is genuinely simpler. After using the conjugate, collect like terms and inspect for remaining common factors, rather than stopping immediately after expansion. A useful result is a form with a rational numerator that is easier to simplify or evaluate than the starting expression.
In a limit that gives 0/0, direct substitution may not reveal the value. Rationalizing the numerator can transform the expression into an equivalent form in which the radical difference is replaced by a rational factor. The resulting form may expose simplification needed for evaluation, making conjugates a practical algebraic tool in limit problems.