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Mathematics·Derivative·grades 10–11

Find the derivative of the function f(x) = x² + 3x

Problem

The function f(x) = x² + 3x is given. Find its derivative f′(x).

Answer

f′(x) = 2x + 3

Step-by-step solution

  1. Step 1. Recall the rule

    The derivative of a sum equals the sum of the derivatives: (u+v)′=u′+v′(u+v)' = u' + v'. So we differentiate each term separately.

  2. Step 2. Derivative of the first term

    For a power function (xn)′=n xn−1(x^n)' = n\,x^{n-1}. Therefore (x2)′=2x(x^2)' = 2x.

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  • Step 3. Derivative of the second term
  • Step 4. Assemble the answer
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Common mistakes

  • Forgetting that the derivative of a constant is zero (there is no constant here, but in f(x)=x²+3x+5 the term 5 disappears).

  • Writing (x2)′=x(x^2)' = x instead of 2x2x — losing the factor from the exponent.

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