Find P C .
Note: This length can be expressed as B A , where A , B are coprime positive integers. Submit the value of A + B as your answer.
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Thinking outside the box. Short and sweet. Excellent approach.
Let P C = x and ∠ A P C = θ , then using sine rule, we have:
sin 9 0 ∘ x = x ⇒ 2 ( sin ( 6 0 ∘ − θ ) ) 2 ( 2 3 cos θ − 2 1 sin θ ) 3 cos θ − sin θ 3 cos θ 3 cos 2 θ 3 ( 1 − sin 2 θ ) 3 ⇒ sin θ ⇒ x ⇒ A + B = sin θ 2 = sin ( 6 0 ∘ − θ ) 3 = 3 sin θ = 3 sin θ = 3 sin θ = 4 sin θ = 1 6 sin 2 θ = 1 6 sin 2 θ = 1 9 sin 2 θ = 1 9 3 = sin θ 2 = 1 9 3 2 = 3 7 6 = 7 6 + 3 = 7 9
verı got...
I used sine rule in the very first step
Brilliant! This is a usual solution. Can you think of other solutions? Shorter ones?
Extend the line BC to intersect extension of line AP at point D.
DAC=30 degrees
CD=2/sin(60)=4
BP=7tan(30)=7/sqrt(3)
CP^2=BP^2+BC^2
CP=sqrt(76/3)
That's what I have used. It's a simple problem though.
P = ( 0 , 0 ) C = ( x , 3 ) A P : y = tan 3 π x ⟹ 3 x − y = 0 3 2 + 1 2 ∣ 3 x − 3 ∣ = 2 ∣ 3 x − 3 ∣ = 2 ⟹ ∣ 3 x − 3 ∣ = 4 ⟹ x = 3 7 Other solution is extraneous C P = x 2 + 9 = 3 4 9 + 9 = 3 7 6 ⟹ 7 6 + 3 = 7 9
Nice use of co-ordinate geometry!
Let the radius be x then x²+x²-2x.xcos120 = 4 + 9 - 2.2.3.cos120. Then x = sqrt(19/3). PC is diameter so PC = 2x = sqrt(76/3). Sry cant use latex im confused
C can be found as intersection of 2 lines:
So the x coordinate of C is 7/sqrt(3)
-> PC=sqrt(3^2 + (7/sqrt(3))^2)=sqrt(76/3)
Here I present a proof using coordinate geometry.
Let P = ( 0 , 0 ) and B = ( b , 0 ) , where b > 0 . Then O = ( b , 3 ) . Now
S l o p e O A = S l o p e O B − 1 = t a n 6 0 ∘ − 1 = − t a n 3 0 ∘ ,
and O A = 2 with A to the left of O so the point A = ( b − 2 c o s 3 0 ∘ , 3 + 2 s i n 3 0 ∘ ) = ( b − 3 , 4 ) .
Now, the slope of P A is t a n 6 0 ∘ = 3 , so
b − 3 4 = 3 , giving b = 3 7 .
Therefore P C = b 2 + 9 = 3 4 9 + 9 = 3 7 6 , and so
A + B = 7 6 + 3 = 7 9 .
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Extend P B and A C , label the point of intersection as E .
We have ∠ A E P = 3 0 ∘ , ⇒ C E = 6 , A E = 8 , ⇒ A P = 3 8 3 , ⇒ P C = 2 2 + ( 3 8 3 ) 2 = 3 2 5 7 = 9 4 × 5 7 = 3 7 6 .