' File XIX_dbl10
' Surface, S, is portion of plane x + 2y + 4z = 0
F{x,y,z} = x + y + z
Z{x,y} = 1 - x/4 - y/2    ' Portion of plane.lying in the first octant.

Dx{x,y} = Diff[Z,x]
Dy{x,y} = Diff[Z,y] 
H{x,y} = F{x,y,Z{x,y}} * Sqrt[1 + Dx{x,y}^2 + Dy{x,y}^2]

' ******************************************
a = 0  :  b = 2  :  C{x} = 0  :  D{x} = 4 - 2x
n = 10  : m = n

s1 = dblInt[H, C, D, {a, b, n, m, x}]
ex = 7Sqrt[21]/3      ' Exact value.


