Monday, July 30, 2018

10:06 AM

Differential Approximation to \Delta F

If 𝛥𝐹 = 𝑓(𝑥) − 𝑓(﷐𝑥﷮0﷯) then Δ𝑓 ≅ ﷐﷐𝑓﷮′﷯﷐﷐𝑥﷮0﷯﷯﷮Δ𝑥﷯


Define function
Calculate partial derivative


Two varianle function roles

What about for z=f(x,y)


If F=F(x,y), x=x(t), y=y(t)

Then...
dF/dt = DF/Dx dx/dt + Df/Dy dy/dt
dF/dt = sum of the products of the derivatives along the branches


If z=F(x,y) = x^2 y + 3xy^4 and x=e^t, y=sin(t) , then use the chain rule to find dz/dt
     X ----------\
   / dz/dx         \   dx/dt
Z                         t
   \ dz/dy         /   dy/dt
      y  ----------/


dz/dt = Dz/Dx dx/dt + Dz/Dy dy/dt

z = x^2 y + 3xy^4
x = e^t
y = sin(t)


Dz/Dx = 2xy + 3y^4
Dz/Dy = x^2 + 3x * 4y^3
dx/dt = e^t
dy/dt = cos(t)

dz/dt = Dz/Dx dx/dt + Dz/Dy dy/dt
…




Chain Rule Formula 2

If F is a function of x and y and x=x(s,t) and y=y(s,t) then...

DF/Dt = Df/Dx  Dx/Dt + DF/Dy Dy/Dt
DF/Dt = Df/Dx  Dx/Dt + DF/Dy Dy/Dt


To get Df/Ds = DF/Dx Dx/Ds + Df/Dy Dy/Ds














Chain Rule Formula 3
If 𝐹=𝐹(𝑢) and 𝑢=𝑢﷐𝑥,𝑦﷯
…





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