+0  
 
0
236
4
avatar+154 

A circle with radius r, is inside an equilateral triangle, with sides x cm 

The circumference of the circle touches each side of the triangle 

The area of the circle is 100 cm^2

Work out the value of x 

Give your answer to 2 significant figures

YEEEEEET  Feb 22, 2018
 #1
avatar+12562 
+1

First find the radius of the circle   area = pi r^2   r = 5.64 cm

Then   tan 30 = 1/2 / (sqrt(3) /2)) = r/(1/2x)   where x is side length

1/2 / sqrt 3/ 2 =  r/(1/2 x)

1/2 x  * .57735 = r   = 5.64    x = 19.53 ~~~ 20 cm (two sig-figs  

 See diagram below:

Ooops ...forgot diagram (and I found an error...fixed)

ElectricPavlov  Feb 22, 2018
edited by ElectricPavlov  Feb 22, 2018
edited by ElectricPavlov  Feb 22, 2018
 #2
avatar+87333 
+1

 

The radius of the circle  is :     sqrt [ (100) / pi ]  =  10 / sqrt (pi)

 

We can find 1/2 of the length of the side of the triangle thusly :

 

[ (1/2)x ] /  sin (60)  =  [10/ sqrt (pi)]  / sin (30)

 

x / [ 2 sqrt (3) /2 ]  =  2 * 10 / sqrt(pi)

 

 x / sqrt (3)   =  20/ sqrt(pi)

 

x =  20 sqrt (3)  / sqrt (pi)   =   20  sqrt (3/pi) ≈ 19.54 cm

 

( 20 cm  rounded to 2 sig figs )

 

 

 

cool cool cool

CPhill  Feb 22, 2018
 #3
avatar+12562 
+1

Here is the diagram I sketched:

ElectricPavlov  Feb 22, 2018
 #4
avatar+4 
+1

The radius of the circle  is :     sqrt [ (100) / pi ]  =  10 / sqrt (pi)

 

We can find 1/2 of the length of the side of the triangle thusly :

 

[ (1/2)x ] /  sin (60)  =  [10/ sqrt (pi)]  / sin (30)

 

x / [ 2 sqrt (3) /2 ]  =  2 * 10 / sqrt(pi)

 

 x / sqrt (3)   =  20/ sqrt(pi)

 

x =  20 sqrt (3)  / sqrt (pi)   =   20  sqrt (3/pi) ≈ 19.54 cm

ruozhoumath  Feb 23, 2018

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