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# Simplifying with Assumptions

 Simplify[expr,assum] simplify expr with assumptions

Simplifying with assumptions.

Mathematica does not automatically simplify this, since it is only true for some values of x.
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is equal to x for x≥0, but not otherwise.
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This tells Simplify to make the assumption x>0, so that simplification can proceed.
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No automatic simplification can be done on this expression.
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If a and b are assumed to be positive, the expression can however be simplified.
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Here is a simple example involving trigonometric functions.
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 Element[x,dom] state that x is an element of the domain dom Element[{x1,x2,...},dom] state that all the xi are elements of the domain dom Reals real numbers Integers integers Primes prime numbers

Some domains used in assumptions.

This simplifies assuming that x is a real number.
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This simplifies the sine assuming that n is an integer.
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With the assumptions given, Fermat's Little Theorem can be used.
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This uses the fact that sin (x), but not arcsin (x), is real when x is real.
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