Find the area of quadrilateral PQRS whose vertices are P(–5, –3), Q(–4, – 6), R(2, –3) and S(1, 2).


For triangle PQR


Area of triangle


= l1/2(x1(y2−y3) + x2(y3−y1) + x3(y1−y2))l


= 1/2(–5(–6 + 3)–4(–3 + 3) + 2(–3 + 6))


= 1/2(15 + 0 + 6)


= 1/2(21)


For triangle PRS


Area of triangle


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


= 1/2(–5(–3–2) + 2(2–(–3)) + 1(–3 + 3))


= 1/2(25 + 10 + 0)


= 1/2(35)


Area of ABCD = Area of ABC + Area of ACD


= 21/2 + 35/ 2


= 28 sq units


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