Odpowiedź:
A = ( - 1 , 2 ) , B = ( 5 , - 1 ) , C = ( 8 , 5 )
xa = - 1 , xb = 5 , xc = 8 , ya = 2 , yb = - 1 , yc = 5
P = 1/2I(xb - xa)(yc - ya) - (yb - ya)(xc - xa)I =
= 1/2I(5 + 1)(5 - 2) - (- 1 - 2)(8 + 1)I = 1/2I6 * 3 - (- 3 * 9)I =
= 1/2I18 - (- 27)I = 1/2I18 + 27I = 1/2I35I = 1/2 * 35 = 17,5 [j²]