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Ncert exercise 12.3_In a circular table …

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Ncert exercise 12.3_In a circular table cover of radius 32 cm, a design is formed leaving an equilateral triangle ABC in the middle as shown in the given figure. Find the area of the design (Shaded region).
  • 1 answers

Gaurav Seth 5 years, 3 months ago

Radius of the circle = 32 cm

Draw a median AD of the triangle passing through the centre of the circle.
⇒ BD = AB/2

Since, AD is the median of the triangle

∴ AO = Radius of the circle = 2/3 AD

⇒ 2/3 AD = 32 cm

⇒ AD = 48 cm
In ΔADB,

<a href="https://3.bp.blogspot.com/-gsz4sf7No4w/VYwFPSkyvbI/AAAAAAAABA4/6QBibJ98sAw/s1600/ch12-class10-maths-area-related-to-circles-6.png" rel="nofollow" target="_blank"></a>

By Pythagoras theorem,

AB= AD2  + BD2 

⇒ AB= 482  + (AB/2)2

⇒ AB= 2304  + AB2/4
⇒ 3/4 (AB2) = 2304

⇒ AB= 3072

⇒ AB = 32√3 cm
Area of ΔADB = √3/4 × (32√3)cm= 768√3 cm2
Area of circle = π R2 = 22/7 × 32 × 32 = 22528/7 cm2

Area of the design = Area of circle - Area of ΔADB

                              = (22528/7 - 768√3) cm2

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