In the diagram above,
O
A
D
is a quarter circle of radius 2.
O
B
and
O
C
trisect arc
A
D
, and
D
E
bisects segment
O
A
. If the area of quadrilateral
W
X
Y
Z
can be expressed in the form
n m ( p − q r )
for positive integers m , n , p , q and r with g cd ( m , n ) = 1 , g cd ( p , q ) = 1 , and r is not divisible by the square of any prime. Find the value of
m + n + p + q + r .
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Great solution! Much more simple than mine!
And yeah... phones + latex never ends well...
I used coordinate geometry to solve the question, however my method is way too long and not appreciable enough to be shared. :|
First, lets break down the diagram into sections in order to get the area of W X Y Z . Let [ a ] denote the area of a .
We can tell by our diagram that
[ △ A O D ] = 2 = [ △ A W O ] + [ △ O Z D ] + [ △ O X Y ] + [ W X Y Z ]
We can also place O at the origin and let O A lie on the y − a x i s and O D lie on the x − a x i s .
We can represent every line that makes up W X Y Z on the diagram as:
O B = y 1 = 3 x O C = y 2 = 3 1 x A D = y 3 = 2 − x D E = y 4 = 1 − 2 1 x
We can find the areas of these triangles by dropping down perpendiculars and using A r e a = B a s e × H e i g h t
To find [ △ A W O ] we need the x-value of y 1 = y 3 , so we get
3 x = 2 − x x = 3 − 1
And by A r e a = B a s e × H e i g h t , we get
[ △ A W O ] = 2 ( 3 − 1 ) ( 2 ) = 3 − 1
To Find [ △ O Z D ] we need the y-value of y 2 = y 3 , so we get
3 1 x = 2 − x = y 2 = y 3 y 2 = y 3 = 3 − 1
And so we can conclude that
[ △ A W O ] = [ △ O Z D ] = 3 − 1
In order to find [ △ O X Y ] , we can see that
[ △ E O D ] = 1 = [ △ O X Y ] + [ △ E X O ] + [ △ O Y D ]
To find △ E X O , we need the x-value of y 1 = y 4 , so we get
3 x = 1 − 2 1 x x = 1 1 2 ( 2 3 − 1 )
So we can conclude that
[ △ E X O ] = 2 ( 1 1 2 ( 2 3 − 1 ) ) ( 1 ) = 1 1 1 ( 2 3 − 1 )
Also, to find [ △ O D Y ] , we need the y-value of y 2 = y 4 , so we get
3 1 x = 1 − 2 1 x = y 2 = y 4 y 2 = y 4 = 4 − 2 3
So we can conclude that
[ △ E X O ] = 4 − 2 3
Now we have everything we need to finish the problem. We get that
[ W X Y Z ] = 2 − [ △ A W O ] − [ △ O Z D ] − [ △ O X Y ] [ W X Y Z ] = 2 − [ △ A W O ] − [ △ O Z D ] − ( 1 − [ △ E X O ] − [ △ O Y D ] ) [ W X Y Z ] = 2 − ( 3 − 1 ) − ( 3 − 1 ) − ( 1 − ( 4 − 2 3 ) − ( 1 1 1 ( 2 3 − 1 ) ) )
After some manipulation we get that
[ W X Y Z ] = 1 1 2 ( 3 8 − 2 1 3 )
This satisfies all of our constraints for m , n , p , q , r , so
m + n + p + q + r = 2 + 1 1 + 3 8 + 2 1 + 3 = 7 5
Used the same method as Mahdi Al-kawaz . I was to give a little more detail. But I think his is sufficient.
However on second thought, coordinate geometry is also a nice method.
OD and OA, X and Y rectangular axis. Then,
Y
O
B
=
3
X
,
Y
O
C
=
3
1
X
,
Y
A
D
=
−
X
+
2
,
1
Y
E
D
+
2
X
E
D
=
1
.
Points of intersections give coordinates of W, X, Y, Z. So the area.
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Using basic facts we can obtain the following:
∠ Z O D = ∠ W O Z = 3 0 ∘ , ∠ A D O = 4 5 ∘ , E D = 5 , sin E D O = 5 1 and O W = O Z .
let ∠ E D O = α ⇒
sin O Y D = sin ( 1 5 0 ∘ − α ) = 2 5 2 + 3
sin O X D = sin ( 1 2 0 ∘ − α ) = 2 5 1 + 2 3 .
Applying the law of sines on the triangles OWD, OXD and OYD we get O W = 1 + 3 4 ,
O X = 1 + 2 3 4 and O Y = 2 + 3 4 respectively.
The area of WXYZ=area of OWZ-area of XOZ = 2 1 × sin 3 0 ∘ × O W × O Z − 2 1 × sin 3 0 ∘ × O X × O Y = 1 1 2 ( 3 8 − 2 1 3 )
Conclusion 1. The answer is 7 5 .
Conclusion 2. Writing a solution using my phone..never again.