MathDB

1964 AMC 12/AHSME

Part of AMC 12/AHSME

Subcontests

(40)

Magnitudes of triangle ABC

The magnitudes of the sides of triangle ABCABC are aa, bb, and cc, as shown, with cbac\le b\le a. Through interior point PP and the vertices AA, BB, CC, lines are drawn meeting the opposite sides in AA', BB', CC', respectively. Let s=AA+BB+CCs=AA'+BB'+CC'. Then, for all positions of point PP, ss is less than:
<spanclass=latexbold>(A)</span>2a+b<spanclass=latexbold>(B)</span>2a+c<spanclass=latexbold>(C)</span>2b+c<spanclass=latexbold>(D)</span>a+2b<spanclass=latexbold>(E)</span><span class='latex-bold'>(A) </span>2a+b\qquad<span class='latex-bold'>(B) </span>2a+c\qquad<span class='latex-bold'>(C) </span>2b+c\qquad<span class='latex-bold'>(D) </span>a+2b\qquad <span class='latex-bold'>(E) </span> a+b+ca+b+c
[asy] import math; defaultpen(fontsize(11pt)); pair A = (0,0), B = (1,3), C = (5,0), P = (1.5,1);
pair X = extension(B,C,A,P), Y = extension(A,C,B,P), Z = extension(A,B,C,P);
draw(A--B--C--cycle); draw(A--X); draw(B--Y); draw(C--Z); dot(P); dot(A); dot(B); dot(C); label("AA",A,dir(210)); label("BB",B,dir(90)); label("CC",C,dir(-30)); label("AA'",X,dir(-100)); label("BB'",Y,dir(65)); label("CC'",Z,dir(20)); label("PP",P,dir(70)); label("aa",X,dir(80)); label("bb",Y,dir(-90)); label("cc",Z,dir(110)); //Credit to bobthesmartypants for the diagram [/asy]

Permissible positions of a circle

In this figure the radius of the circle is equal to the altitude of the equilateral triangle ABCABC. The circle is made to roll along the side ABAB, remaining tangent to it at a variable point TT and intersecting lines ACAC and BCBC in variable points MM and NN, respectively. Let nn be the number of degrees in arc MTNMTN. Then nn, for all permissible positions of the circle:
<spanclass=latexbold>(A)</span>varies from 30 to 90<span class='latex-bold'>(A) </span>\text{varies from }30^{\circ}\text{ to }90^{\circ}
<spanclass=latexbold>(B)</span>varies from 30 to 60<span class='latex-bold'>(B) </span>\text{varies from }30^{\circ}\text{ to }60^{\circ}
<spanclass=latexbold>(C)</span>varies from 60 to 90<span class='latex-bold'>(C) </span>\text{varies from }60^{\circ}\text{ to }90^{\circ}
<spanclass=latexbold>(D)</span>remains constant at 30<span class='latex-bold'>(D) </span>\text{remains constant at }30^{\circ}
<spanclass=latexbold>(E)</span>remains constant at 60<span class='latex-bold'>(E) </span>\text{remains constant at }60^{\circ}
[asy] pair A = (0,0), B = (1,0), C = dir(60), T = (2/3,0); pair M = intersectionpoint(A--C,Circle((2/3,sqrt(3)/2),sqrt(3)/2)), N = intersectionpoint(B--C,Circle((2/3,sqrt(3)/2),sqrt(3)/2));
draw((0,0)--(1,0)--dir(60)--cycle); draw(Circle((2/3,sqrt(3)/2),sqrt(3)/2)); label("AA",A,dir(210)); label("BB",B,dir(-30)); label("CC",C,dir(90)); label("MM",M,dir(190)); label("NN",N,dir(75)); label("TT",T,dir(-90)); //Credit to bobthesmartypants for the diagram [/asy]