Level 3 Differentiation Walkthrough

2023 NCEA Level 3 Differentiation Question 3(b)

2023 Paper

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Question

The graph below shows the function \(y=f(x)\).

Graph of a piecewise function with open circles, turning points, and a V shape on the right
\[ \text{(i) Find the value(s) of }x\text{ where }f(x)\text{ is continuous but not differentiable.} \] \[ \text{(ii) Find the value(s) of }x\text{ where }f'(x)=0\text{ and }f''(x)<0\text{ are both true.} \] \[ \text{(iii) What is the value of }\lim_{x\to 6}f(x)\text{?} \]

First walkthrough idea

Hint to try first

Continuous but not differentiable means the graph is joined up but has a sharp corner.

Step 1

Find the continuous corner

The graph meets at \(x=8\), but it does so with a sharp corner.

Show the first step’s working

The graph meets at \(x=8\), but it does so with a sharp corner.

Key result

\[ x=8 \]

Walkthrough overview

What this question practises

This 2023 walkthrough is part of AS91578 — Apply differentiation methods in solving problems.

Method: Reading continuity, concavity, and limits from a graph.

This is Question 3(b) from the 2023 NCEA Level 3 Differentiation paper for AS91578 — Apply differentiation methods in solving problems. Use the guided hints to practise the method before revealing the full working.

Calc.nz is an independent learning resource. Compare questions, diagrams, and assessment information with the official NZQA resources for AS91578.

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Learning summary

Review the method, not only the answer

This walkthrough helps you practise reading continuity, concavity, and limits from a graph. Use the hints to plan the method, then repeat the question without hints and check each step.

Common mistake to avoid

Check each step against the original condition, preserve signs and restrictions, and confirm that the final result answers the question asked.

Continue practising