A-level Maths revision · Pure, year 1

Standard derivatives

The idea

Bring the power down and reduce it by one: ddx(xn)=nxn−1\frac{d}{dx}(x^n) = nx^{n-1}. Also ddx(ekx)=kekx\frac{d}{dx}(e^{kx}) = ke^{kx}, ddx(ln⁡x)=1x\frac{d}{dx}(\ln x) = \frac{1}{x}, ddx(sin⁡kx)=kcos⁡kx\frac{d}{dx}(\sin kx) = k\cos kx and ddx(cos⁡kx)=−ksin⁡kx\frac{d}{dx}(\cos kx) = -k\sin kx, with xx in radians.

  1. Rewrite roots and fractions as powers: x=x12\sqrt{x} = x^{\frac{1}{2}}, 2x=2x−1\frac{2}{x} = 2x^{-1}.
  2. Differentiate term by term.
  3. Constants differentiate to 00.

Watch out Rewrite 4x2\frac{4}{x^2} as 4x−24x^{-2} before you differentiate.

See it worked

Worked example

Differentiate y=4x3−2x+xy = 4x^3 - \frac{2}{x} + \sqrt{x}.

  1. Rewrite: y=4x3−2x−1+x12y = 4x^3 - 2x^{-1} + x^{\frac{1}{2}}.
  2. Differentiate each term.
  3. dydx=12x2+2x−2+12x−12\frac{dy}{dx} = 12x^2 + 2x^{-2} + \frac{1}{2}x^{-\frac{1}{2}}.

Answer 12x2+2x2+12x12x^2 + \frac{2}{x^2} + \frac{1}{2\sqrt{x}}

Your turn

Question 1Non-calculator3 marks

Differentiate y=5x4−3x2+7y = 5x^4 - 3x^2 + 7.

Question 2Non-calculator3 marks

Differentiate y=6x+4x2y = 6\sqrt{x} + \frac{4}{x^2}.

Question 3Non-calculator3 marks

Differentiate y=e4x+3sin⁡xy = e^{4x} + 3\sin x.

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