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AP EAMCET · Maths · Trigonometric Ratios & Identities

The value of tan7π8 is

  1. A 2-1
  2. B 1-2
  3. C 1+2
  4. D 11+2
Verified Solution

Answer & Solution

Correct Answer

(B) 1-2

Step-by-step Solution

Detailed explanation

Let A=tan7π8 ⇒A=tanπ-π8 ⇒A=-tanπ8 Now, tanπ4=tan2×π8=2tanπ81-tan2π8 ⇒2tanπ81-tan2π8=1 ⇒2-A1--A2=1 ⇒A2-2A-1=0 ⇒A=2±4+42 ⇒A=1±2 But A<0, since 7π8 lies in 2nd…