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The area of a quadrilateral is 227.2 cm2 and the length of the perpendiculars from the opposite vertices to a diagonal are 7.2 cm and 8.8 cm. What is the length of the diagonal ?

  • A.26.8 cm
  • B.28.4 cm
  • C.30.2 cm
  • D.32.6 cm

Answer: B

The diagonal is 28.4 cm.

A diagonal divides the quadrilateral into two triangles with the diagonal as their common base and the two perpendiculars as their heights:

\[ \begin{aligned} \text{Area} &= \tfrac{1}{2} d (h_{1} + h_{2}) \\ 227.2 &= \tfrac{1}{2} d (7.2 + 8.8) = 8d \\ d &= 28.4\ \text{cm} \end{aligned} \]

Forgetting the factor one half gives 14.2 cm, not an option; the other values do not satisfy the area formula (for example 8 × 26.8 = 214.4).

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