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TS EAMCET · Maths · Differentiation

If fx=cos2x1+sin2x, then fπ4-3f'π4=

  1. A 53
  2. B 113
  3. C 139
  4. D 3
Verified Solution

Answer & Solution

Correct Answer

(D) 3

Step-by-step Solution

Detailed explanation

fx=cos2x1+sin2x⇒fπ4=cos2π41+sin2π4=13 ...(1) ⇒lnfx=lncos2x1+sin2x=2lncosx-ln1+sin2x Differentiating both sides w.r.t. x, ⇒f'xfx=-2sinxcosx-2sinxcosx1+sin2x=-2tanx-sin2x1+sin2x Putting x=π4, ⇒f'π4fπ4=-2-11+12=-83…