Page 2-29
Press
‚O
to activate the Equation Writer. Then press
‚½
to enter
the summation sign. Notice that the sign, when entered into the Equation
Writer screen, provides input locations for the index of the summation as well
as for the quantity being summed. To fill these input locations, use the
following keystrokes:
~„k™1™„è™1/~„kQ2
The resulting screen is:
To see the corresponding expression in the line editor, press
‚—
and the
A
soft menu key, to show:
This expression shows the general form of a summation typed directly in the
stack or line editor:
Σ
(
index = starting_value
,
ending_value
,
summation expression
)
Press
`
to return to the Equation Writer. The resulting screen shows the
value of the summation,
To recover the unevaluated summation use
‚¯
. To evaluate the
summation again, you can use the
D
soft menu key. This shows again that
6
1
2
1
2
π
=
∑
∞
=
k
k
.
You can use the Equation Writer to prove that
+∞
=
∑
∞
=
1
1
k
k
.
This summation (representing an infinite series) is said to diverge.
Double summations are also possible, for example:
