Area of triangle formed by angle bisector, altitude and median Question:-
Given a triangle ABC with side length a, b and c. Calculate the area of a triangle in terms of a, b and c formed by angle bisector from vertex A, altitude from vertex B and median from vertex C.
looking for solution using complex number, vectors and co-ordinate geometry
Regards,
vishal


Given $\triangle ABC$, $BC=a,\ AC=b,\ AB=c$;
$\angle BAD=\angle CAD$,
$BE\perp AC$, $AF=BF$,
$\angle BAC=\alpha$,
$\angle BCA=\gamma$.
First, define coordinates of the points $A,B,C,E$ and $F$:
\begin{align}
A &=(0,0),\\
B &=(c\cos\alpha,c\sin\alpha), \\
C &=(b,0),\\
E &=(c\cos(\alpha),0),\\
F &=(c/2\cos\alpha,c/2\sin\alpha) \\
\end{align}
Coordinates of the point $D$ can be defined as follows:
\begin{align}
D_y &= x\tan\gamma = (b-x)\tan\frac{\alpha}{2},
\\
x&=\frac{b}{\tan\gamma+\tan\frac{\alpha}{2}},
\\
D&=\left(
\frac{b}{\tan\frac{\alpha}{2}(1+\tan\frac{\alpha}{2}/\tan\gamma)}
,\frac{b}{1+\tan\frac{\alpha}{2}/\tan\gamma}
\right).
\end{align}
Next, find the intersection points 
$U=AD \cap CF$,
$V=AD \cap BE$,
$W=BE \cap CF$:
\begin{align}
U&=\left(
c b \frac{1+\cos\alpha}{c+2 b}
,
c b \frac{\sin\alpha}{c+2 b}
\right)
\\
V &= \left(
c\cos\alpha, c\cos\alpha\frac{(1-\cos\alpha)}{\sin\alpha}
\right)
\\
W &= \left(c \cos(\alpha),c\sin(\alpha)
\frac{b-c\cos(\alpha)}{2b-c\cos(\alpha)}
\right)
\end{align}
\begin{align}
S_{\triangle UVW}
&=
|(V_x-U_x)(W_y-U_y)-(V_y-U_y)(W_x-U_x)|/2.
\end{align}
Finally, after substitution $\sin\alpha=\sqrt{1-\cos^2\alpha}$,
$\cos\alpha=\frac{b^2+c^2-a^2}{2bc}$ 
and simplification, 
the area of $\triangle UVW$ is given 
in terms of $a,b$ and $c$
by quite a nice construction:
\begin{align}
S_{\triangle UVW}
&=
\frac{1}{4}
\sqrt{\frac{(a-b+c)(a+b-c)}{(a+b+c)(b+c-a)}}
\frac{\left(b^3-b^2 c+b c^2+c^3-a^2 (b+c)\right)^2}
{b|3 b^2-c^2+a^2| (c+2 b)}
.\quad(*)
\end{align}
Test: 
the first triangle: $a=8$, $b=10$, $c=12$,
$S_{\triangle UVW}=3.266386$,
the second triangle: $a=8$, $b=10$, $c=15$,
$S_{\triangle UVW}=16.835510$.
And as expected, when $a=b=c$, $S_{\triangle UVW}=0.$ 
Edit:
Equation (*) also reveals another extreme case, 
when the altitude $BE$ is parallel to the median $CF$ and
$S_{\triangle UVW}=\infty$ due to the condition $3 b^2-c^2+a^2=0$
in the denominator:

Indeed in this case, $c^2-(2b)^2=a^2-b^2$.
