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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
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<b>Expression Editor Help</b>
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<b> General </b>
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The <i>Expression Editor</i> is where you will do most of your work. The nuances of manipulating expressions are covered in the tutorial - return to the tutorial for additional help.
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If you navigated to the <i>Expression Editor</i> from the <i>Expression List Editor</i> the back button will be <i> Expression List</i>. When you touch the back button you will return to the <i> Expression List Editor</i> and any changes made to the expression will be saved in the expression list.
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<b> Change History</b>
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As you change an expression in the <i>Expression Editor</i>, a copy of each step is saved and appears above the active expression. You may back up to a previous step by double tapping on desired step. Note that only the previous 5 steps are displayed, but all previous steps are saved.
<b> Multiply by one </b>
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If a non-equation expression is selected you can multiply that expression by a fractional form of 1 by tapping the "x1" button. x/x, for example, is a fraction that evaluates to one. x can be any non-zero expression. The "x1" button will bring up the expression entry dialog. Enter the expression you wish to use. <i>Pocket Algebra</i> will create a fraction, using the entered expression for the numerator and denominator, and multiply it with the selected expression.
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Example: Assume x has been selected in the following equation: y = 2*x - 3/2. Tap the "x1" button and enter 2 in the expression entry dialog. The fraction 2/2 is created and x is multiplied by 2/2, resulting in y = 2*x*(2/2) - 3/2.
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Important! With this release Pocket Algebra cannot ensure you enter a non-zero expression. For example, the expression c + c - c - c evaluates to zero, which can lead to nonsensical results.
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<b> Adding and subtracting from both sides of an equation </b>
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To add an expression to both sides of an equation select the equation, tap the "+" button and enter the desired expression in the <i>Expression Entry Screen</i>.
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Similarly, to subtract an expression from both sides of an equation select the equation, tap the "-" button and enter the desired expression in the <i>Expression Entry Screen</i>.
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Example: Assume you have selected the following equation: y - 3 = 4*x + 6. To add 3 to both sides of the equation tap the "+" button and enter 3. The resulting equation will be: y - 3 + 3 = 4*x + 6 + 3.
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<b> Multiplying and dividing both sides of an equation </b>
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To multiply both sides of an equation by an expression select the equation, press the "*" button and enter the desired expression in the <i>Expression Entry Screen</i>.
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Similarly, to divide both sides of an equation by an expression select the equation, tap the "/" button and enter the desired expression in the <i>Expression Entry Screen</i>.
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Important! With this release <i>Pocket Algebra</i> cannot ensure you enter a non-zero expression when dividing. For example, expression c + c - c - c evaluates to zero, which can lead to nonsensical results.
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Example: Assume you have selected the following equation: 3*y = 2*x + 9. To divide both sides of the equation by 3 tap the "/" button and enter 3. The resulting equation will be: (3*y)/3 = (2*x + 9)/3.
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<b> Raising both sides of an equation to a power </b>
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To raise both sides of an equation to a power select an equation and tap the "Exp" button. Enter the desired exponent in the <i>Expression Entry Screen</i>.
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Radical roots (i.e. square root) must be entered as fractions. For example, to take the square root of both sides of an equation enter ½ in the <i>Expression Entry Screen</i>.
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Important! Taking the square root of an equation formally results in two equations, usually denoted by ±. With this release <i>Pocket Algebra</i> will only return only a single equation - the principle square root, which is the positive square.
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