Mathematics
Functions
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Question

text  If  end text f subscript n left parenthesis x right parenthesis equals open parentheses tan x over 2 close parentheses left parenthesis 1 plus sec x right parenthesis left parenthesis 1 plus sec 2 x right parenthesis midline horizontal ellipsis open parentheses 1 plus sec 2 to the power of n x close parentheses text end text
Then which of the following is not true?

  1. f subscript 2 left parenthesis pi divided by 16 right parenthesis equals 1
  2. f subscript 3 left parenthesis pi divided by 32 right parenthesis equals 1
  3. f subscript 4 left parenthesis pi divided by 64 right parenthesis equals 1
  4. f subscript 5 left parenthesis pi divided by 128 right parenthesis equals 0

The correct answer is: f subscript 5 left parenthesis pi divided by 128 right parenthesis equals 0


    f subscript n left parenthesis x right parenthesis equals tan x over 2 left parenthesis 1 plus sec x right parenthesis left parenthesis 1 plus sec 2 x right parenthesis horizontal ellipsis open parentheses 1 plus sec 2 to the power of n x close parentheses equals tan x over 2 fraction numerator 1 plus cos x over denominator cos x end fraction times fraction numerator 1 plus cos 2 x over denominator cos 2 x end fraction horizontal ellipsis fraction numerator 1 plus cos 2 to the power of n x over denominator cos 2 to the power of n x end fraction
equals 2 to the power of n plus 1 end exponent sin x over 2 cos x over 2 cos x cos 2 x horizontal ellipsis cos 2 to the power of n minus 1 end exponent x sec 2 to the power of n x equals sin 2 to the power of n x times sec 2 to the power of n x equals tan 2 to the power of n x
f subscript 3 left parenthesis pi divided by 16 right parenthesis equals tan left parenthesis 4 pi divided by 16 right parenthesis equals tan pi divided by 4 equals 1
f subscript 3 left parenthesis pi divided by 32 right parenthesis equals tan left parenthesis 8 pi divided by 32 right parenthesis equals tan pi divided by 4 equals 1
f subscript 4 left parenthesis pi divided by 64 right parenthesis equals left parenthesis 16 pi divided by 64 right parenthesis equals tan pi divided by 4 equals 1
f subscript 5 left parenthesis pi divided by 128 right parenthesis equals tan left parenthesis 32 pi divided by 128 right parenthesis equals tan pi divided by 4 equals 1

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