For a triangle with vertices A(x1,y1), B(x2,y2) and C(x3,y3) answer the following:
a. (i) Write the algebraic expression that gives the area of △ABC directly in terms of the six coordinates.
b. (ii) Explain why this expression is zero when the three points are collinear.
c. (iii) If the coordinates are A(2,5), B(−1,−3) and C(4,1), calculate the numerical value of the expression obtained in part (i) and hence state the area of the triangle.