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MathsMediumMCQ2010 · Unknown

Q72.For a regular polygon, let r and R be the radii of the inscribed and the circumscribed circles. A false statement among the following is (1) There is a regular polygon with 1 (2) There is a regular polygon with r = R R r = 32 √2 (3) There is a regular polygon with Rr = √32 (4) There is a regular polygon with Rr = 21

What This Question Tests

This question tests the relationship between the inradius (r) and circumradius (R) of a regular polygon with 'n' sides, specifically r/R = cos(π/n), and identifying a false statement among the options.

Concepts Tested

Inradius and circumradius of regular polygonsGeometric properties

Formulas Used

r = a / (2 tan(π/n))

R = a / (2 sin(π/n))

r/R = cos(π/n)

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9.17 (a) sin i¢c = 1.44/1.68 which gives i¢c = 59°. Total internal reflection takes place when i > 59° or when r < rmax = 31°. Now, (sin i /sin r max max ) = 1.68 , which gives imax ~ 60°. Thus, all incident rays of angles in the range 0 < i < 60° will suffer total internal reflections in the pipe. (If the length of the pipe is finite, which it is in practice, there will be a lower limit on i determined by the ratio of the diameter to the length of the pipe.) (b) If there is no outer coating, i¢c = sin–1(1/1.68) = 36.5°. Now, i = 90° will have r = 36.5° and i¢ = 53.5° which is greater than i¢c. Thus, all incident rays (in the range 53.5° < i < 90°) will suffer total internal reflections.

📋 Question Details

Chapter
Trigonometric Functions & Equations
Topic
Properties of Regular Polygons
Year
2010
Shift
Unknown
Q Number
Q72
Type
MCQ
NCERT Ref
Class 11 Mathematics Ch 3: Trigonometric Functions

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