Find the area of LABC with A(1, –4) and midpoints of sides through A being (2, –1) and (0, –1).

The diagram is given below:


Coordinates of B


2 = (1 + x)/2 [by section formula]


4 = 1 + x


X = 3


–1 = (–4 + y)/2


–2 = (–4 + y)


Y = 2


the coordinates of B(3,2)


Coordinates of C [by section formula]


0 = (1 + x)/2


0 = (1 + x)


x = –1


–1 = (–4 + y)/2


–2 = (–4 + y)


Y = 2


the coordinates of point C are (–1,2)


Now, Area of triangle ABC


= 1/2(x1(y2−y3) + x2(y3−y1) + x3(y1−y2))


= 1/2(1(2–2) + 3(2 + 4)–1(–4–2))


= 1/2(0 + 18 + 6)


= 1/2(24)


= 12 sq unit


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