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. 2012 May;33(2):49–75.

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The contents of articles or advertisements in The Clinical Biochemist – Reviews are not to be construed as official statements, evaluations or endorsements by the AACB, its official bodies or its agents. Statements of opinion in AACB publications are those of the contributors. Print Post Approved - PP255003/01665. Copyright © 2005 The Australasian Association of Clinical Biochemists Inc. No literary matter in The Clinical Biochemist – Reviews is to be reproduced, stored in a retrieval system or transmitted in any form by electronic or mechanical means, photocopying or recording, without permission. Requests to do so should be addressed to the Editor. ISSN 0159 – 8090

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Figure 1(a). — Points P and Q on the curve y = f (x). Coordinates of P = (x, y), coordinates of Q = (x+δx, y+δy); where δx represents a small change in x and δy the corresponding small change in y. Figure 1(b). As Q approaches P, the distance P to Q along the curve approximates a straight line. When Q is infinitesimallyclose to P, the tangent line to P and Q makes an angle α (alpha) to the x-axis, where tan α equals the derivative dy/dx. This is the derivative of y with respect to x.