In a quadrilateral A B C D , ∠ D A B = ∠ A B C = 1 1 0 ∘ , ∠ B C D = 3 5 ∘ , and A C bisects ∠ D A B .
Find the measure of ∠ A B D in degree measures.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Let I be the Incenter of △ A B D and ∠ A B D = 2 x . ∠ B I D = 9 0 + 2 ∠ A = 1 4 5 ∘ . We can clearly see that Quad. B I D C is cyclic since ∠ B I D + ∠ B C D = 1 4 5 ∘ + 3 5 ∘ = 1 8 0 ∘ . By angle chasing we know that ∠ A C D = 2 0 ∘ = ∠ D B I by cyclic properties. Therefore ∠ A B D = 2 × 2 0 ∘ = 4 0 ∘ .
Problem Loading...
Note Loading...
Set Loading...
Let the ⊙ A D B ∩ A C ≡ O . Now, A O is the bisector of ∠ A D B , therefore, A O bisects arc B D and B O = D O . Also, ∠ D O B = 7 0 ∘ = > O is the circumcenter of Δ D B C .
Clearly, ∠ A O D + ∠ D O C = ∠ A B D + 2 × ∠ D B C = ∠ A B D + 2 × [ ∠ 1 1 0 ∘ − ∠ A B D ] = 1 8 0 ∘ = > ∠ A B D = 4 0 ∘