SOLUTION: Which identity is not used in the proof of the identity 1 + cot^2(theta) = csc^2(theta)?

  

Here's the proof.

By the Pythagorean theorem, in any right triangle,

  

Divide every term by 

  

Use a rule of exponents

  

Therefore

  

We only used the Pythagorean theorem and the definition of the trig
ratios cotangent and cosecant.  There are many identities we did not need to use.

Edwin