Question:
In the given figure, ABCD is a quadrilateral-shaped field in which diagonal BD is 36 m, AL ⊥ BD and CM ⊥ BD such that AL = 19 m and CM = 11 m. Find the area of the field.
Solution:
Area of quadrilateral $\mathrm{ABCD}=($ Area of $\Delta \mathrm{ABD})+($ Area of $\Delta \mathrm{BCD})$
$=\left(\frac{1}{2} \times \mathrm{BD} \times \mathrm{AL}\right)+\left(\frac{1}{2} \times \mathrm{BD} \times \mathrm{CM}\right)$
$=\left[\left(\frac{1}{2} \times 36 \times 19\right)+\left(\frac{1}{2} \times 36 \times 11\right)\right] \mathrm{m}^{2}$
$=(342+198) \mathrm{m}^{2}$
$=540 \mathrm{~m}^{2}$
Hence, the area of the field is $540 \mathrm{~m}^{2}$.