## Solve()

formats:

- solve(expression)
- solve(expression, variable)
- solve([expression1, expression2],[var1,var2])

supplying an expression without any keyword first tries to solve the
expression by default but can be made more effective by using it explicitly.

** the expressions is assumed to be equal to zero**.
In case of numerous variables, the variable to be solved for may be specified,
else one will be chosen automatically, usually x if present. See structure below.
For example, exp(x)+1, exp(x)+1, x and solve(exp(x) + 1, x) all produce the same result
To solve simultaneous equations, first make each equations to be equal to 0, then supply as show below.
solve([eq1,eq2...], [var1,var2...]). For example:

solve([x + 5*y - 2, -3*x + 6*y - 15], [x, y])