Q:        Why does LN(e) not simplify to 1?

A:        In Derive e is just a variable and not the base of the natural logarithms (2.71828...).  The base of the natural logarithms is displayed as an italicized e, and can be entered by clicking on the e on the math symbol toolbar, by pressing Ctrl+E, or by typing #e.


Q:        Why does i^2 not simplify to -1?

A:        In Derive i is just a variable and not the imaginary unit (the square-root of -1).  The imaginary unit is displayed as an italicized i, and can be entered by clicking on the i on the math symbol toolbar, by pressing Ctrl+I, or by typing #i.


Q:        Why does LN(x^2-x)-LN(x) not simplify to LN(x-1)?

A:        This transformation is invalid if x is negative.  However, if you use the Author > Variable Domain command8MNT4Y to declare x nonnegative, Derive will simplify the expression.  In general, Derive will not use a transformation unless it can determine that the transformation is valid.


Q:        How do I turn the name of a function I defined back into a variable name?

A:        Use the Author > Variable Domain command8MNT4Y to declare the name a real-valued variable.


Q:        When I use square brackets when entering expressions like 3·[x+y], why does the result not behave correctly?

A:        In Derive square brackets are used exclusively for entering vectors and matrices.  Thus the above expression is interpreted as 3 times the one element vector [x+y].  Parentheses rather than brackets should be used to control the order in which operators are applied (see Entering Mathematical ExpressionsEntering_Mathematical_Expressions).


Q:        When I integrate the derivative of x/(x+1), why do I get −1/(x+1) instead of the original expression?

A:        Antiderivatives are not unique and may differ by a constant.  In this case x/(x+1) and −1/(x+1) differ by the constant 1, and both are valid antiderivatives.


Q:        Why doesn’t the integral of SIN(t)/t for t=0 to x simplify to the sine integral SI(x)?

A:        Derive returns antiderivatives of expressions only if they can be expressed in terms of the elementary functions and operators and/or the Gamma, Digamma, Error, Zeta, and Dilogarithm functions.  Note that Derive can compute numerical approximations to the integral of SIN(t)/t  when given numerical limits.


Q:        When calling on trig functions, how do I enter angles in degrees? 

A:        In Derive 6, the ° operator is used to enter an angle in degrees.  The ° operator can be entered by clicking on it on the math symbol toolbar, pressing Ctrl+O, or by typing deg on the expression entry line.  For example, SIN(45°) simplifies to √2/2.  Unlike earlier versions of Derive, selecting Degree in the Angular Unit fieldAngular_Unit_field of the Simplification tab of the Options > Mode Settings command only effects the display of angles, not how angles are entered.  


Q:        In approximate mode, how do I get the inverse trig functions to return angles in degrees instead of radians? 

A:        In approximate mode, the built-in inverse trig functions (e.g. ASIN, ACOS, ATAN, etc.) always return angles in radians, even in Degree mode.  For example, in Degree mode ATAN(1) simplifies to 45° but approximates to 0.7853981633.  To always get angles returned in degrees use the inverse trig functions (e.g. ARCSIN, ARCCOS, ARCTAN, etc.) defined in MiscellaneousFunctions.mth144O15P instead of the built-in functions.  For example, ARCTAN(1) simplifies and approximates to 45.


Other Frequently Asked Questions and AnswersFrequently_Asked_Questions_and_Answers 

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