A kite is cut out of card. Its two diagonals cross at right angles and measure 24 cm and 18 cm. Find the area of the kite in ${\text{cm}}^2$.

When the diagonals of a quadrilateral cross at right angles, its area = ½ × d₁ × d₂ = ½ × $24\times 18=216{\text{cm}}^2$. (Multiplying the diagonals without halving gives $432{\text{cm}}^2$; 42 cm is merely their sum, a length.)