Controlling Numerical Evaluation

NHoldAll	prevent any arguments of a function from being affected by N
NHoldFirst	prevent the first argument from being affected
NHoldRest	prevent all but the first argument from being affected

Attributes for controlling numerical evaluation.

Usually N goes inside functions and gets applied to each of their arguments.

Out[1]=

This tells Mathematica not to apply N to the first argument of

Now the first argument of

is left in its exact form.

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