**Part A --- Review of **
**seq**** and introduction of **
**add ****(7 minutes)**

Recall that
*seq *
makes sequences. For example:

`> `
**seq( 3^k, k = 3 .. 15 );**

**Exercise**
(do it now, but not to turn in): use
*seq *
to create the sequence 1,
,
,
,
, ...

`> `
**seq( x^k, k=0..12);**

The
* add *
command works exactly like

`> `
**add( x^k, k = 3 .. 15 );**

**Exercise**
(do it now, but not to turn in): use
*add *
to create the sum
+ ... +

`> `
**add(n*y^n,n=1..13);**

Note that for both
*seq *
and
*add*
:

1. The variable is a "dummy" variable local to the command.

2. The boundaries of the sequence/sum must evaluate to
__explicit numbers__
when the sequence/sum is evaluated.

For example, note the variable
*k*
:

`> `
**k := 3.963;
add( k, k = 1 .. 5 );
k;**

and note that
**the following fails**
(in contrast to the closely related but quite different function
*sum *
that we will investigate later; for now avoid the use of
*sum*
!)

`> `
**restart;
add( k, k = 1 .. n );**

Error, unable to execute add

`> `

`> `
**add((-1)^k*x^k,k=0..8);**

`> `