+0  
 
0
2917
4
avatar

Find the number of distinct triangles with the measurements a=5, b=2, and A=51

 Jul 27, 2015

Best Answer 

 #4
avatar+128407 
+10

Since we have a SSA situation, we could have more than one triangle ...Using the Law of Sines,  we have......

 

sin B / 2 = sin 51 /  5   ...... so......

 

sin-1 ((2/5)* sin 51)  = about 18.11º  = angle B

 

And......subtracting this from 180 we have (180 - 18.11)° =  161.89º.......but....this angle added to the known angle of 51° is greater than 180°, so only one triangle is possible.......as Melody found......

 

The angles are

A = 51  B = 18.11  C = 110.89

 

And side c  =  c / sin 110.89 =  5 /sin 51    ...so....   c = 5(sin110.89) / sin 51   = about 6.01

 

So the sides are  a = 5,  b = 2 and c = 6.01

 

 

  

 Jul 27, 2015
 #1
avatar+118608 
+10

Find the number of distinct triangles with the measurements a=5, b=2, and A=51

 

There appears to only be one.

 Jul 27, 2015
 #2
avatar+33614 
+10

Depends what is meant by "distinct" I guess.  If you reflect Melody's triangle in any of its sides, you get another one that can't be rotated into the first.

.

 Jul 27, 2015
 #3
avatar+118608 
+10

Hi Alan,

It would still be congrent though.

You could translate it too then it would be in a different position so it would not be the same triangle. :)

 Jul 27, 2015
 #4
avatar+128407 
+10
Best Answer

Since we have a SSA situation, we could have more than one triangle ...Using the Law of Sines,  we have......

 

sin B / 2 = sin 51 /  5   ...... so......

 

sin-1 ((2/5)* sin 51)  = about 18.11º  = angle B

 

And......subtracting this from 180 we have (180 - 18.11)° =  161.89º.......but....this angle added to the known angle of 51° is greater than 180°, so only one triangle is possible.......as Melody found......

 

The angles are

A = 51  B = 18.11  C = 110.89

 

And side c  =  c / sin 110.89 =  5 /sin 51    ...so....   c = 5(sin110.89) / sin 51   = about 6.01

 

So the sides are  a = 5,  b = 2 and c = 6.01

 

 

  

CPhill Jul 27, 2015

2 Online Users

avatar