Derousseau's Generalization of the Malfatti circles

Angle Bisectors


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\(\mathbf{1a}\)   \((013)\)

\[\begin{aligned}\overrightarrow{AA^{\prime}} &= \dfrac{1-{\sin\dfrac{A}{2}}+{\cos\dfrac{B}{2}}-{\cos\dfrac{C}{2}}+{\cos\dfrac{A}{2}}-{\sin\dfrac{B}{2}}+{\sin\dfrac{C}{2}}}{2\left(1+{\sin\dfrac{A}{2}}-{\sin\dfrac{B}{2}}+{\sin\dfrac{C}{2}}\right)}\overrightarrow{A{I_A}}\\\overrightarrow{BB^{\prime}} &= \dfrac{1+{\sin\dfrac{A}{2}}-{\cos\dfrac{B}{2}}-{\cos\dfrac{C}{2}}+{\cos\dfrac{A}{2}}-{\sin\dfrac{B}{2}}+{\sin\dfrac{C}{2}}}{2\left(1+{\cos\dfrac{A}{2}}+{\cos\dfrac{B}{2}}+{\sin\dfrac{C}{2}}\right)}\overrightarrow{B{I_A}}\\\overrightarrow{CC^{\prime}} &= \dfrac{1+{\sin\dfrac{A}{2}}+{\cos\dfrac{B}{2}}+{\cos\dfrac{C}{2}}+{\cos\dfrac{A}{2}}-{\sin\dfrac{B}{2}}+{\sin\dfrac{C}{2}}}{2\left(1+{\cos\dfrac{A}{2}}-{\sin\dfrac{B}{2}}-{\cos\dfrac{C}{2}}\right)}\overrightarrow{C{I_A}}\end{aligned}\]

Hiroyasu Kamo