Timeline for answer to A bicentric quadrilateral $ABCD$ by user
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| Mar 29, 2020 at 20:16 | comment | added | user | The idea behind the proof is the following. You probably know that if the cartesian coordinates of two points satisfy the relation $$\frac{y_1}{x_1}=\frac{y_2}{x_2}$$ the points $(x_1,y_1)$ and $(x_2,y_2)$ lie on the line which goes through the origin of the coordinates. The same is valid for skew coordinate systems. In this case the axes are the diagonals $AC$ and $BD$ and their intersection point $K$ is the origin of the coordinates. The essential point in the expression (1) is the symmetry between the angles $\alpha$ and $\beta$. | |
| Mar 29, 2020 at 20:00 | history | edited | user | CC BY-SA 4.0 |
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| Mar 29, 2020 at 7:42 | comment | added | Knowledge Greedy | Thank you for the response! I saw this solution in a Russian journal. I haven’t studied trigonometry. I am not sure I understand what we are trying to prove. What is the idea? | |
| Mar 29, 2020 at 7:38 | history | edited | user | CC BY-SA 4.0 |
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| Mar 29, 2020 at 0:58 | history | answered | user | CC BY-SA 4.0 |