Light from a source A at (−1, 1) is reflected by a plane mirror placed along the x-axis to a receiver B at (2, 2). (a) For a given point (x, 0) between A and B on the x-axis, find the distance between A and (x, 0) and the distance between B and (x, 0). Your answers should depend on x. (b) Denote by D(x) the sum of the two distances you found in the part (a), thought of as a function of x. Find D0 (x). (c) Find the absolute minimum of D(x) on the x-interval [−1, 2]. (d) The light from source A reflected by the mirror to receiver B will travel the shortest distance possible (more precisely, light will obey Fermat’s principle). At what point P on the x-axis between A and B does the light hit the mirror?
Light from a source A at (−1, 1) is reflected by a plane mirror placed along the x-axis
to a receiver B at (2, 2).
(a) For a given point (x, 0) between A and B on the x-axis, find the distance between
A and (x, 0) and the distance between B and (x, 0). Your answers should depend
on x.
(b) Denote by D(x) the sum of the two distances you found in the part (a), thought
of as a function of x. Find D0
(x).
(c) Find the absolute minimum of D(x) on the x-interval [−1, 2].
(d) The light from source A reflected by the mirror to receiver B will travel the
shortest distance possible (more precisely, light will obey Fermat’s principle). At
what point P on the x-axis between A and B does the light hit the mirror?
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