MathDB

5

Part of 2014 China Northern MO

Problems(1)

<HAB=<HAD if ABCD #, I incenter of BCD, H orthocenter of IBD

Source: China Northern MO 2014 p5 CNMO

10/29/2022
As shown in the figure, in the parallelogram ABCDABCD, II is the incenter of △BCD\vartriangle BCD, and HH is the orthocenter of △IBD\vartriangle IBD. Prove that ∠HAB=∠HAD\angle HAB=\angle HAD. https://cdn.artofproblemsolving.com/attachments/4/3/5fa16c208ef3940443854756ae7bdb9c4272ed.png
geometryequal anglesparallelogram