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In triangle ABC, D is the midpoint of BC. Given that AB=3cm, AC=5cm and BC=7cm, find AD.

 Apr 1, 2022

Best Answer 

 #1
avatar+23200 
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I will assume that you can use the Law of Cosines:  c2  =  a2 + b2 - 2·a·b·cos(C).

 

1)  Find the size of angle(B) in triangle(ABC):  b2  =  a2 + c2 - 2·a·c·cos(B).

                     52  =  72 + 32 - 2·7·3·cos(B)

     You now know the size of angle(B)

 

2)  Find the length of side AD in triangle(ABD):

                    AD2  =  32 + 3.52 - 2·3·3.5·cos(B)

 Apr 1, 2022
 #1
avatar+23200 
+1
Best Answer

I will assume that you can use the Law of Cosines:  c2  =  a2 + b2 - 2·a·b·cos(C).

 

1)  Find the size of angle(B) in triangle(ABC):  b2  =  a2 + c2 - 2·a·c·cos(B).

                     52  =  72 + 32 - 2·7·3·cos(B)

     You now know the size of angle(B)

 

2)  Find the length of side AD in triangle(ABD):

                    AD2  =  32 + 3.52 - 2·3·3.5·cos(B)

geno3141 Apr 1, 2022

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