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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<BASEFONT size=6>
<b>Expression Input Screen Help </b>
<br/>
<br/>
The <i>Expression Input Screen</i> is used to enter new expressions.
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<br/>
<b>Important!</b> It is possible to enter an invalid expression! You may enter 2 = 3 if you like - <i>Pocket Algebra</i> cannot ensure the entered expression is mathematically valid. This is the one place where you can make an error using <i>Pocket Algebra</i>, so be careful.
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<b>Entering expressions</b>
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The <i>Expression Input Screen</i> has two keyboards - a character keyboard and a number pad with mathematical operators. Touch the buttons on the alphabetical keyboard to enter letters. Touch the buttons on the numerical keypad to enter numbers and mathematical operators. "x", "y" and "z" are repeated over the number pad for convenience - there is no difference between these buttons and the buttons in the character keyboard.
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When you touch a button the character will be appended in the expression display at the top of the screen. The "Space" button will enter a space; the "Exp" button will enter the exponential symbol "^".
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Use the "x" with the back arrow in the upper left corner of the keypad to delete the right-most character in the expression display window.
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Only single character variables and constants will be accepted. If you enter more than one character, without a space or operator, the second and following characters will be ignored. For example, x + c2 will evaluate to x + c; xyz - 123 will evaluate to x - 123, as so on.
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Use "/" for division, "*" for multiplication, "+" for addition, "-" for subtraction, and "=" for equations.
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Use "Exp" to enter exponential and radical expressions. Radicals are entered using fractional exponents. x^(1/2) is the square root of x. x^(1/3) is the cubed root of x, and so on.
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Use "-" for subtraction, negative numbers (-2) and opposite expressions (-b). Negative and opposite expressions (-3, -x, -(x^2)) must be placed in parenthesis if they are not the first term in an addition or multiplication. -3 - x is ok; -x - (-3) is ok.
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Touch "Clear" to clear the current expression.
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Touch the "Done" button to save the entered expression and return to the previous screen. <b>Important!</b> If you touch the back button you will return to the previous screen and the entered expression will not be saved.
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<b>Rules for entering expressions</b>
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Spaces are optional.
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You cannot enter two operators consecutively.
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An opening parenthesis must be matched with a closing parenthesis.
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Note that in math 4x is shorthand for 4*x. You must use 4*x and not the shorthand notation.
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Real numbers are not supported. Hence, there is no "." character.
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Numbers greater than 9 digits cannot be entered. Any arithmetic that results in a ten-digit number or greater will be ignored.
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You cannot enter zero in the denominator of a fraction. <b>Warning</b> - you CAN enter an expression that evaluates to zero (e.g. 2 - 2). Don't do this.
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<b>Precedence</b>
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The operator precedence is as follows:
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<ol>
<li>Parenthesis (1/2)/3</li>
<li>Exponentials (x^2)</li>
<li>Multiplication and subtraction ("*", "/")</li>
<li>Addition and subtraction ("+", "-")</li>
<li>Negative and opposite expressions (-3, -x)</li>
<li>Equation ("=")</li>
</ol>
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Precedence between "*" and "/" is not guaranteed. In other words, 1/2*3 could be 1/2 times 3 or 1 divided by (2 times 3). Use parenthesis to provide clarity. E.g. (1/2)*3 or 1/(2*3).
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<b>Some examples</b>
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Here are a few examples to demonstrate how to enter more complicated expressions.
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<table border="1">
<tr>
<td>(1/2)*(3/4)</td>
<td>One half times three fourths</td>
</tr>
<tr>
<td>-(x^2) </td>
<td>The opposite of x^2</td>
</tr>
<tr>
<td>(-x)^2 </td>
<td>The opposite of x squared</td>
</tr>
<tr>
<td>-(a^2)*(-(a^2)) </td>
<td>The opposite of a^2 times the opposite of a^2</td>
</tr>
<tr>
<td>(x^(1/2))/(y^(1/2))</td>
<td> The square root of x divided by the square root of y
</td>
</tr>
<tr>
<td>c/(c^(1/2))</td>
<td>c divided by the square root of c</td>
</tr>
<tr>
<td>(1/2)/3 </td>
<td>One half divided by 3</td>
</tr>
<tr>
<td>y + (-x) - (-x) </td>
<td>y plus the opposite of x minus the opposite of x</td>
</tr>
<tr>
<td>y*(x + x)</td>
<td> y times the addition x + x</td>
</tr>
</table>
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<b>Input errors</b>
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<i>Pocket Algebra</i> limits the total number of subexpressions entered to a "reasonable amount" to keep your mobile device from choking on an expression that is too complicated. If you enter too many subexpressions you will receive the error, "Expression is too complex! Sorry - the expression you entered is too complex. Please reduce the number of subexpressions."
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If you enter an invalid expression you will receive the error, "Invalid expression! Sorry - the expression you entered is not valid. Please try again." With this release <i>Pocket Algebra</i> is not going to provide you with meaning help on what you did wrong. The most common input errors are:
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<ol>
<li>You have miss-matched parenthesis. Example: (1/2)/3)*4.</li>
<li>You have entered two operators consecutively because you have have not placed parenthesis around negative or negated expressions. Example: x - -3.</li>
<li>You have a zero in the denominator of a fraction. Example: 2/0.</li>
<li>You have tried to use shorthand for multiplication. Example: 4x instead of 4*x.</li>
<li>You entered a number with 10 or more digits somewhere in the expression.</li>
</ol>
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If you enter a fraction with a zero denominator you will receive the same error as above.
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If you receive an error, delete back to the point of the error, fix the error, and reenter the rest of the expression.
</body>
</html>