IIT JEE 1982 Maths - 'Adapted' - Subjective to Multi-Correct Q3

Geometry Level 3

The number of real solutions of the equation e sin x e sin x 4 = 0 e^{\sin x}-e^{-\sin x}-4=0 divides which of the following options?

  • (A) 4
  • (B) 6
  • (C) 10
  • (D) 12

Enter your answer as a 4 digit string of 1s and 9s - 1 for correct option, 9 for wrong. Eg. 1199 indicates A and B are correct, C and D are incorrect. None, one or all may also be correct.


In case you are preparing for IIT JEE, you may want to try IIT JEE 1982 Mathematics Archives


The answer is 9999.

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1 solution

Sahil Silare
Dec 12, 2016

Let e sin x e^{\sin x} be y y , y 1 y 4 = 0 y-\frac{1}{y}-4=0 y 2 1 4 y = 0 y^2-1-4y=0 y = 2 ± 5 y=2\pm \sqrt{5} e sin x = 2 ± 5 e^{\sin x}=2\pm \sqrt{5} By taking log \log both the sides, sin x = log e ( 2 ± 5 ) \sin x=\log _e\left(2\pm \sqrt{5}\right) As by observation 1 < ( 2 + 5 ) 1<\left(2+\sqrt{5}\right) so x = sin 1 ( 2 + 5 ) x=\sin ^{-1}\left(2+\sqrt{5}\right) is incorrect,

Coming to another solution, x = sin 1 ( 2 5 ) x=\sin ^{-1}\left(2-\sqrt{5}\right) doesn't exists as log of negative numbers are undefined.

So neither of our solution divides the given options hence the answer is 9999.

Shouldn't you start with y 1 y 4 = 0 y-\frac1y-4=0 ?

Shubhamkar Ayare - 4 years, 6 months ago

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I've corrected it.

Sahil Silare - 4 years, 6 months ago

Nice solution. But you made a mistake in the end.

... Coming to another solution,

x = sin 1 ( 2 5 ) x = \sin^{-1} (2-\sqrt5)

x 0.23 r a d x \approx -0.23 \ rad

This is wrong as it was e sin x = 2 5 e^{\sin x} = 2-\sqrt5 . Since, 2 5 2-\sqrt5 is already negative and any power of a positive base in real numbers cannot be negative, therefore, in this case x x is undefined.

Tapas Mazumdar - 4 years, 6 months ago

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OK bro I forgot that log doesn't exists for negative part . XD

Sahil Silare - 4 years, 6 months ago

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You guyz are in Fiitjee raipur right?

Have you started organic chemistry?

Also in which topic are you in physics?

Harsh Shrivastava - 4 years, 6 months ago

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@Harsh Shrivastava Yes. I study in FIITJEE Raipur Harsh. We have started GOC and isomerism and it's about a quarter done. In Physics, we just started Elasticity and SHM. What is the progress in Bhilai?

Tapas Mazumdar - 4 years, 6 months ago

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@Tapas Mazumdar We have just started organic chemistry.In maths we are in complex No's., in physics we are in gravitation.

Harsh Shrivastava - 4 years, 6 months ago

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