## SectionB.3Editing Expressions

### SubsectionOverwriting

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.

###### ExampleB.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.

### SubsectionRecalling an Entry

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

###### ExampleB.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.

### SubsectionInserting 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.

###### ExampleB.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.

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.

###### ExampleB.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.