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Section B.3 Editing Expressions

Subsection Overwriting

We can edit an expression without starting again. If we place the cursor over a symbol and press a new key, the new symbol replaces (overwrites) the old one.

Example B.24

Correct the error in the following keystrokes for \(120 - 36\text{:}\)

\begin{equation*} 120 \, \boxed{(-)} \, 36\, \boxed{\text{ENTER}} \end{equation*}

The calculator gives an error message (See Figure B.23.) Select "2:Goto", and a blinking cursor appears over the error. Press - to replace the negative symbol by the subtraction symbol.

Subsection Recalling an Entry

We can recall a previous entry by pressing 2nd ENTER.

Example B.25

Evaluate \(\sqrt{3}+\sqrt{2}~~ \) and \(~~\sqrt{3}-\sqrt{2} \text{.}\) First evaluate \(\sqrt{3}+\sqrt{2} \text{:}\)

2nd \(\boxed{x^2} ~ 3\,\) ) + 2nd \(\boxed{x^2} ~2\,\) ENTER

Ans. \(3.14626437\)

Now press 2nd ENTER to recall the last entry, and use the left arrow key \(\boxed{\leftarrow}\) to position the cursor over \(+\text{.}\) Press - to change to \({}-{}\text{,}\) then press ENTER. Your screen should look like Figure B.26.

GC with sum and difference of roots
Figure B.26

Subsection Inserting a Character

To insert a new character before a symbol, position the cursor over that symbol and press 2nd DEL to get the INS (insert) command.

Example B.27

Evaluate \(\sqrt{3}-5\sqrt{2} \) by editing the example above.

Press 2nd ENTER to recall the last entry, and use the left arrow key \(\boxed{\leftarrow}\) to position the cursor over the second \(\sqrt{\,}\) from left to right. Press 2nd DEL \(5\) to insert 5 before the \(\sqrt{\,}\) symbol, then press ENTER. Your screen should look like Figure B.28.

GC with sum of roots
Figure B.28

Subsection Recalling an Answer

We often want to use the result from a previous calculation in a new calculation, without having to type in the number. We use the ANS key, 2nd (-), to recall the answer to the last calculation.

Example B.29
  1. Evaluate \(\sqrt{5}-1 \)

    2nd \(\boxed{x^2} ~ 5\,\) ) - \(1 \,\) ENTER

    Ans. \(1.236067977\)

  2. Evaluate \(x^2 + 2x + 1\) for \(x = \sqrt{5}-1 \text{.}\) Because \(x\) is the last answer the calculator computed, we enter

    2nd (-) \(\boxed{x^2}\,\) + \(2\,\) 2nd (-) + \(1 \,\) ENTER

    Ans. \(5\)

    Your screen should look like Figure B.30.

    GC roots minus 1
    Figure B.30