Let's define a few symbols:

In [2]: var('x y z a')
Out[2]: (x, y, z, a)

We use the solve() function to solve equations (the right-hand side is 0 by default):

In [3]: solve(x**2 - a, x)
Out[3]: [-sqrt(a), sqrt(a)]

We can also solve inequalities. Here, we need to use the solve_univariate_inequality() function to solve this univariate inequality in the real domain:

In [4]: x = Symbol('x')
        solve_univariate_inequality(x**2 > 4, x)
Out[4]: Or(x < -2, x > 2)

The solve() function also accepts systems of equations (here, a linear system):

In [5...