Problem with Sine Law: Find the length of the inner bisector of the corner at the top A.

Aysun

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Mar 29, 2019
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Hello!I don’t understand how to do this? If anyone could offer advice, I would appreciate it.

Ex.1 In the triangle ABC are given BC = a, angle B = beta, angle C = gamma. Find the length of the inner bisector of the corner at the top A.
 
Rather difficult to know how to help you without any idea what you know or should know or what you already have imagined.

What are your thoughts? Did you draw a picture?
 
This is the image.
2.png
And I think this should be the solution:

\(\displaystyle \angle\)CAB=180 \(\displaystyle ^\circ\) - (\(\displaystyle \beta\) + \(\displaystyle \gamma\))
\(\displaystyle \Rightarrow\) \(\displaystyle \angle\)CAL=\(\displaystyle \angle\)LAB=\(\displaystyle \frac{180 ^\circ - (\beta+\gamma)}{2}\)

here we use the sines law:

\(\displaystyle \frac{AL}{sin\gamma}\)=\(\displaystyle \frac{CL}{\frac{sin180 ^\circ - (\beta+\gamma))}{2}}\)

\(\displaystyle \Rightarrow\) \(\displaystyle \frac{AL}{sin\gamma}\)=\(\displaystyle \frac{2CL}{sin( \beta+\gamma)}\)

\(\displaystyle \Rightarrow\) AL=\(\displaystyle \frac{2CL.sin \gamma}{sin(\beta+\gamma)}\)

And if I use the sines law for the triangle ALB:

AL=\(\displaystyle \frac{2LB.sin\beta}{sin(\beta+\gamma)} \)

Is it right ? I'm sorry if I have made any mistakes.My English is not that good.
 
What is it that you believe you do not understand?
Did you make any errors on purpose?
 
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