Jim Whitney | Economics 102 |
Notation: X,Y=variables; f,g,u,v=functions of X; b,n=numerical
parameters
Rule (click on Rule number to see proof) | Function | Derivative |
Rule 1: Rule of constants | Y=b | dY/dX = 0 |
Rule 2: Power rule | Y = Xn | dY/dX = nXn-1 |
Rule 3: Rule of coefficients | Y = b u(X) | dY/dX = b du/dX |
Rule 4: Summation rule | Y = u + v | dY/dX = du/dX + dv/dX |
Rule 5: Product rule | Y = u v | dY/dX = u dv/dX + v du/dX |
Rule 6: Quotient rule | Y = u/v |
v du/dX - u dv/dX
dY/dX = ------------------ v2 |
Rule 7: Chain rule | Y = f(u(X)) | dy/dX = dY/du du/dX |
Addendum: Implicit functions
An explicit function of X has the form: Y = f(X)
You can apply the 7 rules directly to explicit functions.
Any other arrangement of terms is called an implicit
function of X. These usually have the form: f(X,Y) = b, where b is a constant.
You can also apply the 7 rules above to implicit functions, as follows:
1. Treat both sides of the equation as explicit
functions and take the derivatives of both sides. Since the righthand side
is a constant, its derivative will equal zero.
2. Anytime you run into an expression containing
Y on the lefthand side, say g(Y), just apply the chain rule: dg/dx = dg/dy
dy/dx.
3. After differentiating, rearrange terms to isolate
dy/dx.