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In a circular table cover of …

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In a circular table cover of radius 32cm a design is formed leaving an equilateral triangle ABC in the middle find the area of the design
  • 1 answers

Sia ? 5 years, 5 months ago

Area of the design (shaded region)
= Area of the circular table cover - Area of the equilateral triangle ABC
{tex}= \pi ( 32 ) ^ { 2 } - \frac { \sqrt { 3 } } { 4 } a ^ { 2 } - ( 1 ){/tex}
Where a cm is the side of the equilateral triangle ABC.
Let h cm be the height of {tex}\Delta A B C{/tex}
Since the centre of the circle coincides with the combined of the equilateral triangle.
Therefore, Radius of the 
circumscribed circle  = {tex}\frac { 2 } { 3 } h \mathrm { cm }{/tex}

According to the question,
{tex}\frac { 2 } { 3 } h = 32 \Rightarrow h = 48{/tex}
Again, {tex}a ^ { 2 } = h ^ { 2 } + \left( \frac { a } { 2 } \right) ^ { 2 }{/tex} ........ By Pythagoras theorem
{tex}\Rightarrow a ^ { 2 } = h ^ { 2 } + \frac { a ^ { 2 } } { 4 }{/tex}
{tex}\Rightarrow \mathrm { a } ^ { 2 } - \frac { \mathrm { a } ^ { 2 } } { 4 } = \mathrm { h } ^ { 2 } = \frac { 3 \mathrm { a } ^ { 2 } } { 4 } = \mathrm { h } ^ { 2 }{/tex}
{tex}\Rightarrow a ^ { 2 } = \frac { 4 h ^ { 2 } } { 3 } \Rightarrow a ^ { 2 } = \frac { 4 ( 48 ) ^ { 2 } } { 3 }{/tex}
{tex}\Rightarrow \mathrm { a } ^ { 2 } = 3072 \Rightarrow \mathrm { a } = \sqrt { 3072 }{/tex}
{tex}\therefore {/tex} Form (1)
Required area {tex}= \pi ( 32 ) ^ { 2 } - \frac { \sqrt { 3 } } { 4 } ( 3072 ){/tex}
{tex}= \frac { 22 } { 7 } ( 1024 ) - 768 \sqrt { 3 } = \left( \frac { 22528 } { 7 } - 768 \sqrt { 3 } \right) \mathrm { cm } ^ { 2 }{/tex}

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