Basics of Trigonometric Derivative

Basics of Trigonometric Derivative

IB AA SL: Core and Optional Content

Core: Sine and cosine derivatives; tangent can be derived using the quotient rule.
Optional: Reciprocal-trigonometric notation and any unintroduced reciprocal-function derivative formulae.

Angles must be in radians.

\(\dfrac{\mathrm d}{\mathrm dx}\sin x=\cos x\qquad\dfrac{\mathrm d}{\mathrm dx}\cos x=-\sin x\)

\(\dfrac{\mathrm d}{\mathrm dx}\tan x=\sec^2x\qquad\cos x\ne0\)

Differentiate the angle as well as the outer trigonometric function.

Example

Differentiate \(\cos(7x)\) with respect to \(x\).

\(\dfrac{\mathrm{d}}{\mathrm{d}x}\cos(7x)\)\({}=-\sin(7x)\cdot7\)\({}=-7\sin(7x)\)

Differentiate \(\tan(5x)\) with respect to \(x\).

\(\dfrac{\mathrm{d}}{\mathrm{d}x}\tan(5x)\)\({}=\sec^2(5x)\cdot5\)\({}=5\sec^2(5x)\)

Differentiate \(\sin(1-3x)\) with respect to \(x\).

\(\dfrac{\mathrm{d}}{\mathrm{d}x}\sin(1-3x)\)\({}=\cos(1-3x)\cdot(-3)\)\({}=-3\cos(1-3x)\)

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Answer:\(\frac{\mathrm{d}}{\mathrm{d}x}\cos(7x)=-7\sin(7x)\), \(\frac{\mathrm{d}}{\mathrm{d}x}\tan(5x)=5\sec^2(5x)\), \(\frac{\mathrm{d}}{\mathrm{d}x}\sin(1-3x)=-3\cos(1-3x)\)

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