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The shorter diagonal of a rhombus with a 70 degree angle is 122 cm long. How long, to the nearest centimeter, is the longer diagonal?

 Jan 19, 2015

Best Answer 

 #1
avatar+128587 
+10

In a rhombus, the diagonals bisect each other as well as the the vertex angles and adjacent angles are supplementary......so assuming that the 70 degree angle is opposite the 122cm diagonal, we have

(1/2 length of the shorter diagonal) / sin (35)  = (1/2 length of the longer diagonal) / sin(55)

Multiply both sides by 2

( length of the shorter diagonal) / sin (35)  = ( length of the longer diagonal) / sin(55)

Multiply both sides by sin(55)

length of the longer diagonal = sin (55) (122 cm) / sin (35) = about 174 cm

Here's a 1/10 scale diagram......

 

 

 

 

 Jan 19, 2015
 #1
avatar+128587 
+10
Best Answer

In a rhombus, the diagonals bisect each other as well as the the vertex angles and adjacent angles are supplementary......so assuming that the 70 degree angle is opposite the 122cm diagonal, we have

(1/2 length of the shorter diagonal) / sin (35)  = (1/2 length of the longer diagonal) / sin(55)

Multiply both sides by 2

( length of the shorter diagonal) / sin (35)  = ( length of the longer diagonal) / sin(55)

Multiply both sides by sin(55)

length of the longer diagonal = sin (55) (122 cm) / sin (35) = about 174 cm

Here's a 1/10 scale diagram......

 

 

 

 

CPhill Jan 19, 2015
 #2
avatar+118608 
+5

You are becoming an expert with GeoGebra Chris 

 Jan 20, 2015
 #3
avatar+128587 
+5

Not really......I just fool around with it until it looks like something reasonable....!!!

 

 Jan 20, 2015
 #4
avatar+118608 
+5

Yes that is how it is learned.  

The more you know the easier it is to add to that knowledge too.   

 Jan 20, 2015

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