Level 3 Integration Walkthrough

2022 NCEA Level 3 Integration Question 2(b)

2022 Paper

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Question

\[ \text{Find the value of }k,\text{ given that }\int_{1}^{k}\frac{2}{\sqrt{x}}\,dx=8. \]

You must use calculus and show the results of any integration needed to solve the problem.

First walkthrough idea

Focus to try first

Turn the radical into a negative power, evaluate the definite integral, then solve the resulting equation for \(k\).

Step 1

Rewrite the integrand

The power rule is easiest to use when the square root is written as an exponent.

Show the first step’s working
\[ \frac{2}{\sqrt{x}}=2x^{-1/2} \]

Walkthrough overview

What this question practises

This 2022 walkthrough is part of AS91579 — Apply integration methods in solving problems.

Method: Solving for an upper limit from a definite integral.

This is Question 2(b) from the 2022 NCEA Level 3 Integration paper for AS91579 — Apply integration 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 AS91579.

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Learning summary

Review the method, not only the answer

This walkthrough helps you practise solving for an upper limit from a definite integral. 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