Plot the following custom function?

Questions
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1

I am trying to plot this function with Plot3D and ContourPlot and they both give blank boxes. Is there something wrong with my code?

f[x_, y_] =  4*Sin[x - 2] + 4*Cos[y - 4] + 9*x^2 - 5*xy + 1*y^2 - 2*x + 4*y
2

Try

f[x_, y_] := 4Sin[x - 2] + 4Cos[y - 4] + 9x^2 - 5x*y + 1y^2 - 2x + 4*y ;
Plot3D[f[x,y],{x,-Pi,Pi},{y,-Pi,Pi}]
3

Hi Katelyn,

You did not post the code you tried so it is not possible to identify what is wrong with it.

f[x_, y_] := 4 Sin[x - 2] + 4 Cos[y - 4] + 9 x^2 - 5 x y + 1 y^2 - 2 x + 4*y
Plot3D[Evaluate@f[x, y], {x, -2 Pi, 2 Pi}, {y, -2 Pi, 2 Pi}]

8257plot.png
8257plot.png450×350 42 KB

4

I suggest you use the delayed evaluation “:=”. For example,If we set x=1;the define a function x+2 with direct assignment and delayed assignment,respectively.The following answer we will get.

360截图16800418293752.png
360截图16800418293752.png533×559 5.04 KB

5

Note that including Evaluate in the Plot expression cuts the time roughly in half (on my system, from around 0.293 sec to around 0.017 sec).

This should hardly matter — except, say, if you were going to be changing the function or the plot range dynamically within a Manipulate.