HP 33s - Manual (Page 342)

E–4 More about Integration
Keys: Display: Description:
| H
 Select equation mode.
L X z 
%º% 1¾ Enter the equation.
L X | `
‘

%º% 1.%2 End of the equation.
| 
/

/  Checksum and length.
‡
 Cancels Equation mode.
Set the display format to SCI 3, specify the lower and upper limits of integration as
zero and 100
499
, than start the integration.
Keys: Display: Description:
{ } 3
0 ‘ a 499


  _
Specifies accuracy level
and limits of integration.
| H
%º% 1.%2 Selects Equation mode;
displays the equation.
|  X ! !
³ /
)


Approximation of the
integral.
The answer returned by the calculator is clearly incorrect, since the actual integral
of f(x) = xe
–x
from zero to
∞
is exactly 1. But the problem is not that
∞
was
represented by 10
499
, since the actual integral of this function from zero to 10
499
is very close to 1. The reason for the incorrect answer becomes apparent from the
graph of f(x) over the interval of integration.