#3 Other equations as identities

[Ted Dunning]

It would be nice if other equations could be used as
identities in simplifying or manipulating equations.

This would, for instance, let me enter some identities
of my own that are useful in a particular setting and
use them as if they were real identities. This is
particularly useful when trying to reduce an equation
using approximations.

[Anonymous]

Note: I am a user, not the developer.

You may already have this ability, but may not be obvious. Try this:

1. Create an equation "E = m c^2".
2. Create another equation "F = m a".
3. Solve the first equation for m (m should be on the left side of the equation).
4. Right-click on the second equation (e.g., in the left pane that lists the equations) and choose "Apply substitution".

A clumsier method is to simply double-click on the "m" in your second equation (or right-click and choose Edit) and enter a "new expression" for your substitution.

[Anonymous]

This isn't the same as an identity.

For instance sin^2 theta + cos^2 theta = 1 is an identity, but you can't solve for a unique value of theta.