Three of these are wrong. Find the one that holds.

Exercise and reference answers

Questions

1. Question

   Three of these identities are false.

   Choices

   1. Item

      1 + cot²x = cosec²x

      Correct

      Yes

   2. Explanation

      sec goes with tan, not cot.

      Item

      1 + cot²x = sec²x

   3. Explanation

      The identity is a SUM, not a difference.

      Item

      cos²x − sin²x = 1

   4. Explanation

      Cosine is even, so the sign does not flip.

      Item

      cos(−x) = −cos x

Explanation