Area and Perimeter of Plane Figures — MATHEMATICS STD 9 — Question
ICSE BoardEnglish MediumSTD 9MATHEMATICSArea and Perimeter of Plane Figures3 Marks
Question
The diagonal of a rectangular plot is $34 \ m$ and its perimeter is $92 \ m$. Find its area.
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Answer
Let a and $b$ be the sides of the rectangle
Since the perimeter is $92\ m$, we have,
$2( a + b ) = 92$
$\Rightarrow a + b = 46\ m ...(1)$
Also, given that diagonal of a trapezium is $34\ m.$
$\Rightarrow a^2 + b^2 = 34^2....(2)$
We know that
$( a + b )^2 - a^2 - b^2 = 2ab$
From equations $(1)$ and $(2)$, we have,
$46^2 - 34^2 = 2ab$
$\Rightarrow 2ab = 960$
$\Rightarrow ab=\frac{960}{2}$
$\Rightarrow ab = 480\ m^2.$
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