In △ A B C , A C = 4 , B C = 5 , and A B = 6 , point E is on A B so that A E = 2 1 E B .
If the sums of C E and the measure of the segment from E to the midpoint of C B can be written as: 2 1 P + Q R , where P , Q , R are all integers. Find P .
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Basically same as Mr. Guilherme Niedu and MR. Marta Reece but little different.
A
E
=
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B
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4
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C
A
B
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C
A
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A
B
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A
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C
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6
4
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+
6
2
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5
2
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9
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A
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C
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4
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2
4
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+
2
2
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2
=
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∴
C
E
=
1
1
.
I
n
Δ
C
E
B
,
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d
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a
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E
M
=
2
1
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2
1
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(
C
E
2
+
6
2
−
5
2
)
=
2
1
2
9
.
∴
C
E
+
E
M
=
2
1
4
4
+
2
1
2
9
=
2
1
4
4
+
2
9
+
Q
R
⟹
P
=
7
3
.
.
△ A B C we get c o s ( C A B ) = 2 × 4 × 6 4 2 + 6 2 − 5 2 = 1 6 9
FromFrom △ A E C and again the law of cosines x = 4 2 + 2 2 − 2 × 2 × 4 × c o s ( C A B ) = 1 1
Again from △ A B C comes c o s ( A B C ) = 2 × 5 × 6 5 2 + 6 2 − 4 2 = 4 3
And from △ D E B we calculate y = 2 . 5 2 + 4 2 − 2 × 2 . 5 × 4 × c o s ( A B C ) = 2 2 9
So x + y = 1 1 + 2 2 9 .
This is a perfectly good answer. It does not, however, fit the required format. To do that, we have to show what it is a squire root of, in other words square it and put that under a square root. With a little simplification, that becomes.
x + y = 2 1 7 3 + 4 3 1 9 .
We can directly apply Stewart's theorem.
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and appolonius theorem which is the special case of it.
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Let us define as F the midpoint of B C . A E = 2 , B E = 4 , B F = C F = 2 . 5 . By cosine law:
B C 2 = A C 2 + A B 2 − 2 ⋅ A C ⋅ A B c o s ( A ^ )
2 5 = 1 6 + 3 6 − 4 8 c o s ( A ^ )
c o s ( A ^ ) = 1 6 9
A C 2 = A B 2 + B C 2 − 2 ⋅ A B ⋅ B C c o s ( B ^ )
1 6 = 2 5 + 3 6 − 6 0 c o s ( B ^ )
c o s ( B ^ ) = 4 3
C E 2 = A C 2 + A E 2 − 2 ⋅ A C ⋅ A E c o s ( A ^ )
C E 2 = 1 6 + 4 − 9
C E = 1 1
E F 2 = B E 2 + B F 2 − 2 ⋅ B E ⋅ B F c o s ( B ^ )
E F 2 = 4 2 5 + 1 6 − 1 5
E F = 2 2 9
C E + E F = 1 1 + 2 2 9
C E + E F = ( 1 1 + 2 2 9 ) 2
C E + E F = 1 1 + 4 2 9 + 3 1 9
C E + E F = 2 1 7 3 + 4 3 1 9
A = 7 3 , B = 4 , C = 3 1 9