MATH 241 -- Multivariable Calculus 

October 23, 2007 

 

 

The following plots show the graph of a function f(x,y), 

together with the graphs of its Taylor polynomials of degree 

1 and degree 2.    Here is the function  f 

 

`:=`(f, proc (x, y) options operator, arrow; `+`(`*`(`^`(x, 3)), `-`(`*`(2, `*`(x, `*`(`^`(y, 2))))), `*`(3, `*`(`^`(x, 2))), `*`(2, `*`(`^`(y, 2))), x) end proc); 1 

proc (x, y) options operator, arrow; `+`(`*`(`^`(x, 3)), `-`(`*`(2, `*`(x, `*`(`^`(y, 2))))), `*`(3, `*`(`^`(x, 2))), `*`(2, `*`(`^`(y, 2))), x) end proc (1)
 

 

The graph of  f  alone: 

 

plot3d(f(x, y), x = -2 .. 2, y = -2 .. 2, axes = boxed, transparency = .85); 1 

Plot
 

This computes the first degree Taylor polynomial at  (a,b) = (0,0): 

 

`:=`(p1, proc (x, y) options operator, arrow; `+`(f(0, 0), `*`((D[1](f))(0, 0), `*`(x)), `*`((D[2](f))(0, 0), `*`(y))) end proc); 1 

proc (x, y) options operator, arrow; `+`(f(0, 0), `*`((D[1](f))(0, 0), `*`(x)), `*`((D[2](f))(0, 0), `*`(y))) end proc (2)
 

 

Here is the plot of  f  and the first degree Taylor polynomial.  The  

graph of  p1  is the tangent plane at  (a,b) = (0,0). 

 

plot3d([f(x, y), p1(x, y)], x = -2 .. 2, y = -2 .. 2, axes = boxed, transparency = [0, .6], style = [patchnogrid, patchnogrid]); 1
plot3d([f(x, y), p1(x, y)], x = -2 .. 2, y = -2 .. 2, axes = boxed, transparency = [0, .6], style = [patchnogrid, patchnogrid]); 1
 

Plot
 

This computes the second degree Taylor polynomial at  (0,0): 

 

`:=`(p2, proc (x, y) options operator, arrow; `+`(p1(x, y), `*`(`/`(1, 2), `*`((D[1, 1](f))(0, 0), `*`(`^`(x, 2)))), `*`((D[1, 2](f))(0, 0), `*`(x, `*`(y))), `*`(`/`(1, 2), `*`((D[2, 2](f))(0, 0), `*`... 

proc (x, y) options operator, arrow; `+`(p1(x, y), `*`(`/`(1, 2), `*`((D[1, 1](f))(0, 0), `*`(`^`(x, 2)))), `*`((D[1, 2](f))(0, 0), `*`(x, `*`(y))), `*`(`/`(1, 2), `*`((D[2, 2](f))(0, 0), `*`(`^`(y, 2... (3)
 

The graph of the second degree polynomial alone: 

 

plot3d(p2(x, y), x = -2 .. 2, y = -2 .. 2, axes = boxed, style = patchnogrid); 1 

Plot
 

The graphs of  f  and its second degree Taylor polynomial together. 

 

plot3d([f(x, y), p2(x, y)], x = -2 .. 2, y = -2 .. 2, axes = boxed, transparency = [.3, .6], style = [patchnogrid, patchnogrid], color = [blue, cyan])
plot3d([f(x, y), p2(x, y)], x = -2 .. 2, y = -2 .. 2, axes = boxed, transparency = [.3, .6], style = [patchnogrid, patchnogrid], color = [blue, cyan])
 

Plot