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← 2020 HSC Extension 1 paper Question 10

Variation 3 · answer guide

Rates of change — Read dQ from chain

Question

If and with , then equals

This practice question was inspired by Question 10 in the 2020 NSW HSC Mathematics Extension 1 examination, © NESA. It is an original TestMum variation that practises the same mathematical idea, not an official NESA question.

Step by step

  1. Set up the solution: write the geometric constraint, differentiate every changing quantity with respect to time, then substitute., so .
  2. Match the result to the choices and state the correct option.Therefore option A is correct.

Common mistake: changing so many features that the new example no longer tests the same mathematical idea.

Verification: cancels.

Any mark labels are a TestMum study aid, not an official NESA marking allocation.

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