HP 15C Uživatelský manuál Strana 251

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Appendix E: A Detailed Look at f 251
t think (naively
in this case, as you'll see) that you should represent the upper limit of
integration by 10
99
which is virtually the largest number you can key into
the calculator. Try it and see what happens.
Key in a subroutine that evaluates the function f(x) = xe
-x
Keystrokes
Display
000-
Program mode.
´ b 1
001-42,21, 1
002- 1 6
'
003- 12
*
004- 20
| n
005- 43 32
Set the calculator to Run mode. Then set the display format to i 3 and
key the limits of integration into the X- and Y-registers.
Keystrokes
Display
Run mode.
´i 3
Sets display format to i 3.
0 v
0.000 00
Keys lower limit into Y-
register.
99
1 99
Keys upper limit into X-
register.
´ f 1
0.000 00
Approximation of integral.
The answer returned by the calculator is clearly incorrect, since the actual
integral of f(x) = xe
-x
from 0 to is exactly 1. But the problem is not that
you represented by 10
99
since the actual integral of this function from 0 to
10
99
is very close to 1. The reason you got an incorrect answer becomes
apparent if you look at the graph of f(x) over the interval of integration:
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