# Modeling, Functions, and Graphs

## 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 $$120 - 36\text{:}$$
$$\qquad\qquad 120$$ (-) $$36$$ ENTER
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 x^2 ) + 2nd x^2 $$2$$ ENTER
Ans. $$3.14626437$$
Now press 2nd ENTER to recall the last entry, and use the left arrow key 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 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.

1. Evaluate $$\sqrt{5}-1$$
2nd 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 (-) x^2 + $$2\,$$ 2nd (-) + $$1 \,$$ ENTER
Ans. $$5$$