Exponential and logarithmic derivatives

Fact: B(x) = bx is continuous.

Fact: B (0) = lim 0 b0+ -b0 exists.

Fact: there is a unique value 𝒆 such that

E (0) = ( 𝒆x ) | x=0 =1

If (x)= 𝒷x then

(x)= (0) 𝒷x

If (x)= x then

( g(x) ) = g(x) g(x)

If x>0 and y=lnx then

y= [lnx] = 1x

If g(x)>0 and h(x)= ln ( g(x) ) then

h (x) = 1 g(x) g (x)

Let b>0, b1

  • If y= logbx then y= 1 xlnb
  • If y= bx then y= bx lnb

Examples

Compute derivatives of

  • sin( x2+5x )

  • x2 x

Compute derivatives of

  • ln( x2 sinx )

  • ln( x2 sin( x3+4x ) 2x+1 )

Compute derivatives of

  • 2x 3x+1
  • log5 ( 4x+9 )

Logarithmic differentiation

Examples

Compute derivatives

  • y= xr
  • y= xx
  • y= ( 2x4+1 ) tanx
  • y= x23 1+x2 x+x3