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分科攻略 · By subject · 5 min

Mathematics: analytic geometry without tears

Standard-form conversion is a mechanical skill. Chord-length problems reduce to a small number of substitutions.

Analytic geometry problems on this paper are long but they are made of short, learnable moves. Recognise which move the question is asking for and the problem shrinks.

The first move is always to write the curve in standard form: x²/a² + y²/b² = 1 for an ellipse, x²/a² − y²/b² = 1 for a hyperbola. Identify a, b, and c. Half the work of most problems is done here.

For chord-length problems, substitute the line into the curve, use Vieta's formulas for x₁+x₂ and x₁x₂, then apply |AB| = √(1+k²) · |x₁ − x₂|. This template solves an enormous fraction of the questions on this topic.

For focus-related questions, the definition (sum or difference of distances to the two foci) is often faster than coordinate bashing. When the question mentions a focus, try the definition first.

Draw the curve. Every time. A sketch of an ellipse takes ten seconds and stops you writing a hyperbola formula for an ellipse question.

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