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Mathematics·Derivative·grades 10–11

Find the derivative of the function f(x) = x·ln(x)

Problem

The function f(x) = x·ln(x) is given. Find its derivative f′(x).

Answer

f′(x) = ln(x) + 1

Step-by-step solution

  1. Step 1. This is a product

    The function is a product of two factors: u=xu = x and v=ln⁡xv = \ln x. The rule: (uv)′=u′v+uv′(uv)' = u'v + uv'.

  2. Step 2. Differentiate each factor

    u′=(x)′=1u' = (x)' = 1, and v′=(ln⁡x)′=1xv' = (\ln x)' = \dfrac{1}{x}.

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  • Step 3. Substitute into the formula
  • Step 4. Answer
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Common mistakes

  • Differentiating factor by factor as u′⋅v′u'\cdot v' — that is wrong, the product rule is required.

  • Not cancelling x⋅1x=1x\cdot\frac1x = 1 and leaving a clumsy answer.

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