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  1. If a2 sec2x – b2 tan2x = c2 then the
    value of (sec2x + tan2x) is equal to (assume b2 ≠ a2)
    1. b2 − a2 +2c2
      b2 + a2
    2. b2 + a2 − 2c2
      b2 − a2
    3. b2 − a2 − 2c2
      b2 + a2
    4. b2 − a2
      b2 + a2 + 2c2
Correct Option: B

a2 sec2x – b2 tan2x = c2
⇒  a2 (1 + tan2x) – b2 tan2x = c2
⇒  a2 + a2tan2x – b2 tan2x = c2
⇒  a2tan2x – b2 tan2x = c2 – a2
⇒  tan2x(a2 – b2) = c2 – a2

⇒  tan2x =
c2 – a2
a2 – b2

∴  sec2x + tan2x
= 1 + tan2x + tan2x
= 1 + 2 tan2x
= 1 +
2(c2 – a2)
a2 – b2

=
a2 – b2 + 2c2 – 2a2
a2 – b2

=
– b2 + 2c2 – a2
a2 – b2

=
b2 + a2 – 2c2
b2 – a2



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