AZ

Hi AZ:

The technique when "solving" a trig identity is to start with the identity and
work on both sides until you get the two sides equal. The "proof" of the
identity then proceeds by starting with this final, true statement and
progressing backwards, through the sequence of steps you have, to arrive at the
identity. In the first part of this process you can of course work on both sides
as long as each resulting equation is true **if and only if** the previous one
is true. There are obvious pitfalls in this type of argument and the two
column format is used as a preventative measure.

Harley.

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