Y by FaThEr-SqUiRrEl, vvluo, samrocksnature, icematrix2, megarnie, mathleticguyyy, mathlearner2357, centslordm, HWenslawski, Lamboreghini, jmiao, Rounak_iitr, Mr_GermanCano
Rectangles
and
are erected outside an acute triangle
Suppose that
Prove that lines
and
are concurrent.




![\[\angle BC_1C+\angle CA_1A+\angle AB_1B=180^{\circ}.\]](http://latex.artofproblemsolving.com/3/3/7/3378f0c4409d14bc0afddf2616992c13f624be3b.png)



This post has been edited 1 time. Last edited by franchester, Apr 15, 2021, 5:18 PM