# Difference between revisions of "2021 USAMO Problems/Problem 1"

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− | + | Rectangles <math>BCC_1B_2,</math> <math>CAA_1C_2,</math> and <math>ABB_1A_2</math> are erected outside an acute triangle <math>ABC.</math> Suppose that<cmath>\angle BC_1C+\angle CA_1A+\angle AB_1B=180^{\circ}.</cmath>Prove that lines <math>B_1C_2,</math> <math>C_1A_2,</math> and <math>A_1B_2</math> are concurrent. |

## Latest revision as of 14:20, 21 April 2021

Rectangles and are erected outside an acute triangle Suppose thatProve that lines and are concurrent.