lesson
State what a function promises
1 · Learn
A function contract describes inputs, expected output and conditions that must hold. A function that returns a value is different from one that only displays it. Clear contracts make components easier to test and reuse.
For a function called square(n), a suitable contract might accept a number and return n × n without changing other data. The name alone does not guarantee the implementation meets that contract.
2 · Worked example
Python def square(n): return n * n returns 25 for square(5). Printing 25 inside a function is not the same as returning 25 to its caller.
3 · Your turn
What should square(-3) return under this contract?
Check your answer
9.
4 · Apply your learning
Write tests for zero, a positive and a negative input, then compare the returned value with the expected one.
Adult guidance and safety
Use an approved sandbox with invented data. Never ask for real passwords, personal records or access to another person's system. These text examples need executable projects and assessed evidence in two languages; reading code alone is not practical mastery.
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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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Year 9 Computing learning routine
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