Let A B C be a 6-8-10 triangle. Call the points of intersection of adjacent angle trisectors of different angles be X , Y and Z . Find (to 3 decimal places) the area of X Y Z .
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I just used brute force after plotting the triangle on a Cartesian Plane. I just banged out Point-Slope equations to find X,Y and Z (with paper and pencil (and calculator for trig ratios and long division) - and it took about half an hour using basic algebra techniques). I was humbled to see that XYZ is an equilateral triangle. There's got to be a simpler way.
link text
L
e
t
α
=
∠
X
/
3
,
β
=
∠
Y
/
3
,
γ
=
∠
Z
/
3
.
T
h
e
c
i
r
c
u
m
r
a
d
i
u
s
R
=
4
∗
a
r
e
a
X
Y
Z
x
y
z
=
4
∗
2
1
∗
6
∗
8
6
∗
8
∗
1
0
=
5
.
I
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h
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a
b
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v
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l
i
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k
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h
e
Δ
X
Y
Z
i
s
n
a
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e
d
a
s
Δ
P
Q
R
,
a
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d
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i
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a
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r
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a
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s
i
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.
T
h
e
f
o
r
m
u
l
a
g
i
v
e
n
i
s
P
Q
=
8
∗
S
i
n
(
α
)
∗
S
i
n
(
β
)
∗
S
i
n
(
γ
)
.
I
n
o
u
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c
a
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t
h
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s
w
o
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l
d
t
r
a
n
s
l
a
t
e
i
n
t
o
,
X
Y
=
8
R
∗
S
i
n
(
α
)
S
i
n
(
β
)
S
i
n
(
γ
)
B
u
t
M
o
r
l
e
y
′
s
T
h
e
o
r
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m
s
t
a
t
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t
h
a
t
t
h
i
s
i
s
a
n
e
q
u
i
l
a
t
e
r
a
l
Δ
.
∴
t
h
e
a
r
e
a
o
f
X
Y
Z
=
4
3
∗
{
R
∗
S
i
n
(
α
)
S
i
n
(
β
)
S
i
n
(
γ
)
}
2
⟹
a
r
e
a
o
f
X
Y
Z
=
4
3
∗
{
5
∗
S
i
n
(
3
S
i
n
−
1
.
8
)
∗
S
i
n
(
3
S
i
n
−
1
.
6
)
∗
S
i
n
(
3
S
i
n
−
1
1
)
}
2
a
r
e
a
o
f
X
Y
Z
=
0
.
7
2
6
2
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Let r be circumradius of △ A B C ,
α = ∠ A / 3 , β = ∠ B / 3 , γ = ∠ C / 3
Side of a Morley triangle is:
s = 8 r ∗ sin ( α ) sin ( β ) sin ( γ ) = 8 ∗ 5 ∗ sin ( 3 0 ) sin ( arctan ( 3 / 4 ) / 3 ) sin ( arctan ( 4 / 3 ) / 3 ) ≈ 1 . 2 9 5
A r e a = 4 3 s 2 ≈ 0 . 7 2 6