HP 15c Scientific manual Keystrokes Display, 001-42,21 002- 1 003 004 005

Models: 15c Scientific

1 288
Download 288 pages 6.63 Kb
Page 251
Image 251

Appendix E: A Detailed Look at f 251

Since you’re evaluating this integral numerically, you might think (naively in this case, as you'll see) that you should represent the upper limit of integration by 1099 – 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

 

¥

 

 

´i 3

 

 

0 v

0.000

00

‛99

1

99

´ f 1

0.000

00

Run mode.

Sets display format to i3.

Keys lower limit into Y- register.

Keys upper limit into X- register.

Approximation of integral.

The answer returned by the calculator is clearly incorrect, since the actual integral of f(x) = xe-xfrom 0 to ∞ is exactly 1. But the problem is not that you represented ∞ by 1099 since the actual integral of this function from 0 to 1099 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:

Page 251
Image 251
HP 15c Scientific manual Keystrokes Display, 001-42,21 002- 1 003 004 005