Functions How Do You Find / Use Function? 

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| x | or abs  Absolute Value Function abs

[MATH] [F1: NUM] [F5: abs] or

[2nd] [CATALOG] F1 abs [ENTER]

Example: | x - 4|: abs ( [x-VAR] - 4 )
The n-th Root Function 

[MATH] [MISC] 

Example: : 3 13 or

13 ^ (1/3)
ISECT The Intersection Function: Find the x-y coordinates of the intersection of two functions visable in the Calculator's Viewing Window:

First Graph the 2 Functions (after selecting ISECT move the cursor to as closed as possible to the intersection of the functions and press ENTER several times until you see the ISECT solution.

[GRAPH] => [F1: MATH] => ISECT

Example
EVAL The Evaluate Function, EVAL: Find the value of the selected Function at x =?

[GRAPH] => EVAL