Porisma

Differentiate standard functions

Retain inner factors, radian assumptions and logarithm domains.

Trigonometric derivatives use radians

Identify the inner function before choosing a derivative. Use radian input, keep the inner derivative as a factor, then check where the original function is defined.

For a differentiable inner function u, all six source rows are:

Function: sin⁡u\sin u

  • Derivative with respect to x: cos⁡u u′\cos u\,u^{\prime}

Function: cos⁡u\cos u

  • Derivative with respect to x: −sin⁡u u′-\sin u\,u^{\prime}

Function: tan⁡u\tan u

  • Derivative with respect to x: sec⁡2u u′\sec^2u\,u^{\prime}

Function: sec⁡u\sec u

  • Derivative with respect to x: sec⁡utan⁡u u′\sec u\tan u\,u^{\prime}

Function: csc⁡u\csc u

  • Derivative with respect to x: −csc⁡ucot⁡u u′-\csc u\cot u\,u^{\prime}

Function: cot⁡u\cot u

  • Derivative with respect to x: −csc⁡2u u′-\csc^2u\,u^{\prime}

Setting u=x gives the source’s basic column.

The source spells csc as cosec and shades the basic secant/cosecant rows as listed in MF27.

Preserve the relevant nonzero sine/cosine denominators.

Degrees would introduce an additional angle-conversion factor; these displayed formulas assume radians.

Exponentials and logarithms

The four source rows, including their general inner-function forms, are:

Function: eue^u

  • Derivative with respect to x: euu′e^u u^{\prime}

Function: aua^u

  • Derivative with respect to x: auln⁡a u′a^u\ln a\,u^{\prime}

Function: ln⁡u\ln u

  • Derivative with respect to x: u′/uu^{\prime}/u

Function: log⁡au=ln⁡u/ln⁡a\log_a u=\ln u/\ln a

  • Derivative with respect to x: u′/(uln⁡a)u^{\prime}/(u\ln a)

The exponential base is positive.

A real logarithm additionally needs u>0 and base a>0, a≠1.

Setting u=x gives every printed basic formula.

Simplifying an answer does not change its original domain: for example, the identity used in Example 7(b) is valid only where its tangent/secant expression exists.

Try these examples

Open an example in chapter practice. Try it first, then read its solution. Use “Learn this step” to return to this unit.

Apply this idea

Nested derivatives and increasing intervals →Differentiate each layer of the composite, then use the quotient rule to find increasing intervals.