Exact value or decimal? Treat the requested format as part of the problem

Many mathematics errors happen after the main reasoning is finished. The solver reaches the right quantity, converts it too early, and submits an approximation where the question expects an exact expression.

Before calculating, copy the requested output into a small answer contract.

• Object. The value, interval, set, probability, or expression being requested.
• Form. An exact expression, simplified fraction, decimal, or proof.
• Conditions. Domain restrictions, units, and required justification.

Keep symbolic forms such as radicals, fractions, and logarithms until the last line unless the prompt explicitly asks for a decimal. Early rounding can hide equality and can also make later checking harder. If a numerical approximation is useful for intuition, write it beside the exact form rather than replacing it.

The untimed 2026 Shanghai mathematics question mode makes a good place to practise this habit. It draws from a source-linked English question collection without forcing a countdown, so the output requirement can be inspected before speed becomes a factor. The site also identifies the material as independently reconstructed and translated rather than an official answer key.

One final check is enough. Compare the last line with the noun phrase in the question. If the prompt asks for a solution set, a single number may be incomplete. If it asks for an exact value, a rounded decimal may be the wrong form even when it is numerically close. Formatting is not decoration here; it is one of the mathematical constraints.