Solve for x ,
sin [ 2 cos − 1 { cot ( 2 tan − 1 x ) } ] = 0
If x has n solutions, all of which can be represented in surd form, x i = a i + b i
Evaluate ⎩ ⎨ ⎧ n + i = 1 ∑ n ( ∣ a i ∣ + ∣ ∣ ∣ b i ∣ ∣ ∣ ) ⎭ ⎬ ⎫
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sin ( e x p ) = 0 does not only imply e x p = 0 .
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You are correct. I am adding to my solution. Please correct the answer.
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What can I do for you? I did not quite understand...
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@Kishore S. Shenoy – My solution and answer I have corrected. So the old answer must be corrected. As the author I think you can correct the answer. Is my solution correct ?
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@Niranjan Khanderia – I can't correct my answer and I don't think your answer is correct. I see a slight mistake in it...
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@Kishore S. Shenoy – Yes. I have made a mistake again !! I missed the first 2 inside. You are correct. I am correcting my mistake. Thank you.
Let's take the expression, sin [ 2 cos − 1 { cot ( 2 tan − 1 x ) } ] = 0
For cos − 1 x Principle domain is θ ∈ [ 0 , π ] ⇒ 2 θ ∈ [ 0 , 2 π ]
So, θ = 0 , 2 π , π . Applying cos , cot { 2 tan − 1 x } = 1 , 0 , − 1
OR 2 x 1 − x 2 = 1 , 0 , − 1
Solving, n = 6 x 1 , x 2 x 3 , x 4 x 5 , x 6 = − 1 ± 2 = ± 1 = 1 ± 2
What makes this problem interesting?
@Calvin Lin What else that these key points such as Bijective domain and all...LOL!!
@Calvin Lin Sir, could you please answer the Moderator's question.....
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S i n [ 2 ∗ C o s − 1 { C o t ( 2 ∗ T a n − 1 X ) } ] = 0 , ⟹ 2 ∗ C o s − 1 { C o t ( 2 ∗ T a n − 1 X ) } = 0 , o r 2 ∗ π O R π . . . . . . . . . . . . . . 0 ≤ 2 ∗ C o s − 1 { C o t ( 2 ∗ T a n − 1 X ) } ≤ 2 ∗ π . ⟹ C o s − 1 { C o t ( 2 ∗ T a n − 1 X ) } = 0 , o r π O R 2 π . ⟹ C o t ( 2 ∗ T a n − 1 X ) = 1 , o r − 1 O R 0 . L e t θ = 2 ∗ T a n − 1 X , ⟹ X = T a n 2 θ . ∴ T a n θ = 1 − X 2 2 X . ⟹ 2 X 1 − X 2 = C o t θ = C o t ( 2 ∗ T a n − 1 X ) . ∴ 2 X 1 − X 2 = ± 1 O R 0 . S o l v i n g t h e q u a d r a t i c , n = 6 , X 1 = − 1 + 2 , X 2 = − 1 − 2 . X 3 = 1 + 2 , X 4 = 1 − 2 . X 5 = 1 , X 6 = − 1 . { n + i = 1 ∑ n ( ∣ a i ∣ + ∣ ∣ b i ∣ ∣ ) } = 6 + 2 ∗ ∣ − 1 ∣ + 2 ∗ ∣ ± 2 ∣ + 2 ∗ ∣ 1 ∣ + 2 ∗ ∣ ± 2 ∣ + 2 ∗ ∣ ± 1 ∣ = 1 7 . 6 5 7