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arildno said:You can derive it, by expanding one variable by one.
f(h+x_0, k+y_0)=f(x_0,y_0+k)+f_x(x_0,y_0+k)h+1/2f_xx(x_0,y_0+k)h^2+++
=f(x_0,y_0)+f_y(x_0,y_0)k+1/2f_yy(x_0,y_0)k^2+f_xy(x_0,y_0)hk+1/2f_xx(x_0,y_0)h^2+++
Where the terms up to second order can be rearranged into the desired equation.
arildno said:First, I make a one-variable Taylor-expansion of the function in x, at the point (x_0,y_0+k).
Then, I make a one-variable expansion in y of the different terms.
elemis said:I have to be truthful, my professor used a similar method to what you described but I just can't see how he used two variables in a Taylor expansion since I've only ever learned to deal with Taylor expansions of one variable.
Could you please break this down further for me ? I would be very much obliged.
arildno said:Well, but when you do partial derivatives, you regard the other variable to be a CONSTANT.
Agreed?
Thus, the function f(x,y), evaluated at the 2-D point (x_0+h,y_0+k) may be regarded as a single-variable function of x along the (horizontal) length segment from (x_0, y_0+k) to (x_0+h, y_0+k).
Along THAT line segment, we may perfectly well expand the function in its Taylor series relativ to "x".
At whatever places "y" stands in the expression for "f" itself.elemis said:Yes, I agree and understand what you mean.
The difficulty I'm having is how do I introduce the constant y_0+k into my taylor expansion ?
The basic formula for a partial derivative is: fx(x,y) = limh→0 (f(x+h,y)-f(x,y))/h where fx represents the partial derivative of f with respect to x, and h is a small change in the x direction.
A partial derivative measures the rate of change of a multivariable function with respect to only one of its variables, while a regular derivative measures the rate of change with respect to a single variable. In other words, a partial derivative considers all other variables constant, while a regular derivative takes into account the effect of all variables on the function.
Yes, a partial derivative can be negative. A negative partial derivative indicates that the function is decreasing in the direction of the variable being considered, while a positive partial derivative indicates that the function is increasing in that direction.
Partial derivatives are useful for understanding how a multivariable function changes in a specific direction. They are also used in optimization problems, where the goal is to find the maximum or minimum value of a function.
No, partial derivatives have applications in various fields such as physics, economics, and engineering. They are used to model real-world processes and make predictions about how these processes will change under different conditions.