lesson
A retry should not duplicate the effect
1 · Learn
An idempotent operation has the same intended effect when repeated with the same request identity. This matters when a client retries because it did not receive confirmation, even though the server may already have completed the first request.
A timeout does not prove nothing happened. Use an explicit operation identity or a safe state check rather than blindly creating a second record.
2 · Worked example
If a submission was saved but the response was lost, a retry using the same operation key can return the existing result instead of creating a duplicate.
3 · Your turn
Does a client timeout prove the server did not save the request?
Check your answer
No. The save may have completed before the response was lost.
4 · Apply your learning
Design a test that repeats one fictional submission request and verifies only one submission is created.
Adult guidance and safety
Use an approved sandbox, invented data and test accounts. Do not probe other systems or expose credentials. Retain test evidence and accessibility checks; these teaching models are not a completed practical project or a specified GCSE qualification.
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Check a calculation · Year 5 onward
Use this only when your teacher or adult allows a calculator for the task. Show your thinking first. It does not replace mental or written arithmetic and does not mark your lesson answer.
Powers, roots and trigonometry · Year 7 onward
Use only when the task allows a calculator. Choose one operation at a time and record your working. Trigonometry here always uses degrees (DEG), not radians. Inverse sine, cosine and tangent return an angle, not a reciprocal. Keep exact fractions and π in answers when requested.
Approximate numerical results use up to 12 significant digits. Inverse sine returns −90° to 90°, inverse cosine 0° to 180°, and inverse tangent −90° to 90°; these are principal values, not every possible solution of a trigonometric equation.
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