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MathsMediumMCQ2023 · 13 Apr Shift 2

Q68.If lim = 17, then 5𝑎2 + 𝑏2 is equal to 𝑥→0 1 - cos ( 2𝑥) (1) 64 (2) 72 (3) 68 (4) 76

What This Question Tests

This question tests the evaluation of a limit of an indeterminate form (0/0) requiring multiple applications of L'Hopital's rule or series expansion to determine unknown coefficients.

Concepts Tested

LimitsL'Hopital's RuleMaclaurin series expansions

Formulas Used

lim (f(x)/g(x)) = lim (f'(x)/g'(x))

e^x ~ 1+x+x^2/2!

cos(x) ~ 1-x^2/2!

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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.