I was working on a geometry problem relating to the angle bisectors of triangles : In triangle

rigliztetbf

rigliztetbf

Answered question

2022-06-13

I was working on a geometry problem relating to the angle bisectors of triangles :

In triangle Δ   A B C,   A = 40 ° ,   B = 20 ° ,   and   A B B C = 4  . Find the length of angle bisector from   C   .

I was able to figure out a majority of the angle measures, but I was unable to utilize the information about the side lengths to find the angle bisector.

Does anyone what method I have to use to solve this?

Answer & Explanation

Patricia Curry

Patricia Curry

Beginner2022-06-14Added 15 answers

Second solution by using sine rule: Let the angle bisector intersects with |AB| on D
sin C sin A = sin 120 sin 40 = sin ( 40 + 80 ) sin 40 = cos 80 + 2 cos 2 40 = 1 + 2 cos 80 = x + 4 x = 1 + 4 x
Thus,
4 x = 2 cos 80
Again by using sine rule on B C D ,
x | D C | = sin 80 sin 20 = sin 80 sin 160 = 1 2 cos 80
Thus,
| D C | = 4
Davon Irwin

Davon Irwin

Beginner2022-06-15Added 5 answers

Let the angle bisector intersects with | A B | on D and take a point, E on | A B | such that E C B = 80 . Then, | B E | = | B C | , | A E | = 4 E C A = 40 which gives us | E C | = 4. Also E C D = 20 , D E C = 80 and E D C = 80 Thus, | C D | = | E C | = 4

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