Difference between revisions of "1981 AHSME Problems/Problem 20"
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A ray of light originates from point <math>A</math> and travels in a plane, being reflected <math>n</math> times between lines <math>AD</math> and <math>CD</math> before striking a point <math>B</math> (which may be on <math>AD</math> or <math>CD</math>) perpendicularly and retracing its path back to <math>A</math> (At each point of reflection the light makes two equal angles as indicated in the adjoining figure. The figure shows the light path for <math>n=3</math>). If <math>\measuredangle CDA=8^\circ</math>, what is the largest value <math>n</math> can have? | A ray of light originates from point <math>A</math> and travels in a plane, being reflected <math>n</math> times between lines <math>AD</math> and <math>CD</math> before striking a point <math>B</math> (which may be on <math>AD</math> or <math>CD</math>) perpendicularly and retracing its path back to <math>A</math> (At each point of reflection the light makes two equal angles as indicated in the adjoining figure. The figure shows the light path for <math>n=3</math>). If <math>\measuredangle CDA=8^\circ</math>, what is the largest value <math>n</math> can have? | ||
− | [asy] unitsize(1.5cm); pair D=origin, A=(-6,0), C=6*dir(160), E=3.2*dir(160), F=(-2.1,0), G=1.5*dir(160), B=(-1.4095,0); draw((-6.5,0)--D--C,black); draw(A--E--F--G--B,black); dotfactor=4; dot("<math>A< | + | <math>[asy] unitsize(1.5cm); pair D=origin, A=(-6,0), C=6*dir(160), E=3.2*dir(160), F=(-2.1,0), G=1.5*dir(160), B=(-1.4095,0); draw((-6.5,0)--D--C,black); draw(A--E--F--G--B,black); dotfactor=4; dot("</math>A<math>",A,S); dot("</math>C<math>",C,N); dot("</math>R_1<math>",E,N); dot("</math>R_2<math>",F,S); dot("</math>R_3<math>",G,N); dot("</math>B<math>",B,S); markscalefactor=0.015; draw(rightanglemark(G,B,D)); draw(anglemark(C,E,A,12)); draw(anglemark(F,E,G,12)); draw(anglemark(E,F,A)); draw(anglemark(E,F,A,12)); draw(anglemark(B,F,G)); draw(anglemark(B,F,G,12)); draw(anglemark(E,G,F)); draw(anglemark(E,G,F,12)); draw(anglemark(E,G,F,16)); draw(anglemark(B,G,D)); draw(anglemark(B,G,D,12)); draw(anglemark(B,G,D,16)); [/asy]</math> |
<math>\textbf{(A)}\ 6\qquad\textbf{(B)}\ 10\qquad\textbf{(C)}\ 38\qquad\textbf{(D)}\ 98\qquad\textbf{(E)}\ \text{There is no largest value.}</math> | <math>\textbf{(A)}\ 6\qquad\textbf{(B)}\ 10\qquad\textbf{(C)}\ 38\qquad\textbf{(D)}\ 98\qquad\textbf{(E)}\ \text{There is no largest value.}</math> |
Revision as of 19:20, 23 October 2021
Problem
A ray of light originates from point and travels in a plane, being reflected
times between lines
and
before striking a point
(which may be on
or
) perpendicularly and retracing its path back to
(At each point of reflection the light makes two equal angles as indicated in the adjoining figure. The figure shows the light path for
). If
, what is the largest value
can have?
A
C
R_1
R_2
R_3
B