; Test if a point in triangle's plane is inside the triangle
(defun C:II( / p0 pp1 pp2 pp3 area alpha beta gama)
	(setq p0 (getpoint "\nSelect TEST point: "))
	(setq pp1 (getpoint "\nSelect 1st TRIANGLE point: "))
	(setq pp2 (getpoint "\nSelect 2nd TRIANGLE point: "))
	(setq pp3 (getpoint "\nSelect 3rd TRIANGLE point: "))
	
	; get triangle area
	(setq area (triarea pp1 pp2 pp3))
	
	; area of subtriangles over area of main triangle
	(setq alpha (/ (triarea p0 pp1 pp2) area))
	(setq beta (/ (triarea p0 pp2 pp3) area))
	(setq gama (/ (triarea p0 pp1 pp3) area))
	
	;(setq gama (- 1 (+ alpha beta)))
	
	(if 
	(= 
	(and (>= alpha 0) (<= alpha 1)) 
	(and (>= beta 0) (<= beta 1)) 
	(and (>= gama 0) (<= gama 1)) 
	(equal (+ alpha beta gama) 1 0.0001) 
	(= 1 1)
	)
		(princ "\nPoint is inside the triangle")
		(princ "\nPoint is outside the triangle")
	)
	
	(princ)
	
)

; Area of a triangle according to Heron's formula
(defun triarea ( p1 p2 p3 / side1 side2 side3 p area)

	(setq
	side1 (distance p1 p2)
	side2 (distance p2 p3)
	side3 (distance p3 p1)
	)
	
	; get half of triangle perimeter
	(setq p (/ (+ side1 side2 side3) 2))
	
	; calculate triangle area
	(setq a (sqrt (* p (- p side1) (- p side2) (- p side3))))
)

(princ)