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 Find the length of the side of a regular pentagon inscribed in the circle of radius 12cm

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THE DIFFERENCE OF THE SQUARES OF TWO SIDES OF A TRIANGLE IS EQUAL TO TWICE THE PRODUCT OF THE THIRD SIDE AND THE PROJECTION OF THE MEDIAN ONTO THE THIRD SIDE.

I.E. GIVEN: TM MEDIAN, TA ALTITUDE ABOVE

PROVE: B(SQUARED)-A(SQUARED)=2 TIMES C TIMES P

WHOLE PROOF WITH JUSTIFICATIONS PLEASE

 Apr 11, 2015

Best Answer 

 #3
avatar+118723 
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This looks like 2 or 3 totally unrelated questions to me.

Pentagon?     triangle?      

Is this a serious question - Am I missing something ?

 Apr 13, 2015

3+0 Answers

 #1
avatar+130516 
+5

For the first one, we can use the Law of Cosines  to find the side length, s

s^2  = (2*12^2) - (2*12*2)* cos 72       

s^2  = about 199  ....   take the square root of both sides

s =  about  14.1

 

  

 Apr 12, 2015
 #2
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Sorry Phil, but thats wrong. Its 16.9706

 Apr 12, 2015
 #3
avatar+118723 
+5
Best Answer

This looks like 2 or 3 totally unrelated questions to me.

Pentagon?     triangle?      

Is this a serious question - Am I missing something ?

Melody Apr 13, 2015

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