Question

Find the area of the quadrilateral whose vertices are A(–3, 1), B(–2, –2), C(4, 1), D(2, 3).

Answer 1

A(–3, 1), B(–2, –2), C(4, 1), D(2, 3)

A(`square`ABCD) = A(ΔABC) + A(ΔACD)

Area of triangle = `1/2|(x_1, y_1, 1),(x_2, y_2, 1),(x_3, y_3, 1)|`

A(ΔABC) = `1/2|(-3, 1, 1),(-2, -2, 1),(4, 1, 1)|`

= `1/2[-3(-2 - 1) - 1(-2 - 4) + 1(-2 + 8)]`

= `1/2(9 + 6 + 6)`

∴ A(ΔABC) = `21/2` sq. units'.

∴ A(ΔACD) = `1/2|(-3, 1, 1),(4, 1, 1),(2, 3, 1)|`

= `1/2[-3(1 - 3) - 1(4 - 2) + 1(12 - 2)]`

= `1/2(6 - 2 + 10)`

∴ A(ΔACD) = 7 sq. units

∴ A(`square`ABCD) = A(ΔABC) + A(ΔACD)

= `21/2 + 7`

= `35/2` sq. units.