Question: How to i write this as a function?

okay so the question i have to answer is "write a maple function that computes the area of a triangle in the plane from the coordinates of the vertices"  

ive gotten this far 

 

with(geometry);

triangle(ABC, [point(A, 0, 0), point(B, 2, 0), point(C, 1, 3)]);

area(ABC);    3

 

but how can i write so when you type say AA([[0,0],[10,10],[10,0]])  it returns  50?  (AA being the function name)

 

Thanks in advance to whoever helps.

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