[RESOLVED]Diff - differential

[Han]

Your equation z=3x^2-xy+y^2 is not a differential equation. Are there differentials in there that you left out, perhaps?

The diff() command computes the derivative (or partial derivative) of an expression. Usually it takes two parameters: an expression, and a variable of differentiation.

For example: diff(x^2*y^3,x) returns 2x*y^3 whereas diff(x^2*y^3,y) returns 3x^2*y^2.

If you do not specify a variable, then the default variable 'x' is used. For example, diff(x^2*y^3) returns 2x*y^3. So in your second attempt, it is not clear what you meant by the diff(diff(..)) operation since you did not specify a variable. Did you mean to compute \( \frac{\partial^2}{\partial x^2} (3x^2-xy+y^2) \) or did you intend to have something else?

In particular, if you have questions on how to use a command, consider using the built-in help:

1) type the command
2) with the cursor on the typed command name, press the help button

Usually, the help also provides examples of how to use the commands. For desolve, the help says:

Code:

Syntax:
desolve(Eq,[TimeVar],Var)

Returns the solution to a differential equation.


Examples:
desolve(y''+y=0,y) → G_0*cos(x)+G_1*sin(x)
desolve((y''+y=sin(x)) and (y(0)=1) and (y'(0)=2),y)