Difference between revisions of "2013 AMC 12A Problems/Problem 19"
Fowlmaster (talk | contribs) (→Solution 2) |
|||
Line 11: | Line 11: | ||
Therefore, the answer is '''D) 61.''' | Therefore, the answer is '''D) 61.''' | ||
− | === | + | |
+ | ==Solution 2== | ||
+ | Let <math>h</math> be the perpendicular from <math>B</math> to <math>AC</math>, <math>AX=x</math>, <math>XC=y</math>, then by Pythagorean Theorem, | ||
+ | |||
+ | <math>h^2 + (x/2)^2 = 86^2</math> | ||
+ | |||
+ | <math>h^2 + (x/2 + y)^2 = 97^2</math> | ||
+ | |||
+ | Subtracting the two equations, we get <math>(x+y)y = (97-86)(97+86)</math>, | ||
+ | |||
+ | then the rest is similar to the above solution by power of points. | ||
+ | |||
+ | ==Solution 3== | ||
Let <math>x</math> represent <math>BX</math>, and let <math>y</math> represent <math>CX</math>. Since the circle goes through <math>B</math> and <math>X</math>, <math>AB</math> = <math>AX</math> = 86. | Let <math>x</math> represent <math>BX</math>, and let <math>y</math> represent <math>CX</math>. Since the circle goes through <math>B</math> and <math>X</math>, <math>AB</math> = <math>AX</math> = 86. | ||
Then by Stewart's Theorem, | Then by Stewart's Theorem, |
Revision as of 12:22, 12 February 2013
Let CX=x, BX=y. Let the circle intersect AC at D and the diameter including AD intersect the circle again at E. Use power of a point on point C to the circle centered at A.
So CX*CB=CD*CE x(x+y)=(97-86)(97+86) x(x+y)=3*11*61.
Obviously x+y>x so we have three solution pairs for (x,x+y)=(1,2013),(3,671),(11,183),(33,61). By the Triangle Inequality, only x+y=61 yields a possible length of BX+CX=BC.
Therefore, the answer is D) 61.
Solution 2
Let be the perpendicular from to , , , then by Pythagorean Theorem,
Subtracting the two equations, we get ,
then the rest is similar to the above solution by power of points.
Solution 3
Let represent , and let represent . Since the circle goes through and , = = 86. Then by Stewart's Theorem,
(Since cannot be equal to 0, dividing both sides of the equation by is allowed.)
The prime factors of 2013 are 3, 11, and 61. Obviously, . In addition, by the Triangle Inequality, , so . Therefore, must equal 33, and must equal 61.
-Solution 2 by fowlmaster