Recent content by behappy

Thanks a lot for your co-operation, I am so interested in what you have just said, but how I can take the absolute value of the function if the domain is [-inf,inf] for both x and y. And also, I use Mathematica so I have plotted the function and the result is a surface. Can I tell whether the...

I have put three different values for x (-20,0,20), so I got a function of y. After that I plotted the new function and the graph shows that it is positive and negative. After that, I put the same values in the original function but now for y and I plotted the new function for x, and that shows...

Sorry, I could not open the attached file. And the graph would be a surface, so I can not tell anything from this.

Right, picking numbers is an easy way to show if a function is neither positive nor negative. But what about the other cases like when the function is always positive

What do you mean by conditions here?

You mean I just need to put random numbers into the equation for both x and y. But that would only work if the function is neither positive nor negative.

And how can I do that?

So, can you tell me please how you found out that it is neither positive nor negative. When I have a function of two variables, I just need to determine whether it is postive or negative.

This is one of them... f(x,y)=x^2 + sin(y) - x y - 4y^3

Hello everbody I have functions of two variables and I need to determine if they are positive or negative. I am just wondering if anyone can tell me what the best way to do that is? Thanks a lot in advance