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You can define equations using SymPy using symbolic math variables. Equations in SymPy are different than expressions. An expression does not have equality. An expression is a collection of symbols and operators, but expressions are not equal to anything. Equations have equality. An equation can be thought of as an expression equal to something else.

A code section that defines the equation 4x + 2 = 0 is below. Note all equations defined in SymPy are assumed to equal zero.

In [1]:
from sympy import symbols, Eq

x = symbols('x')

eq1 = Eq(4*x+2)

If you want to define the equation 2y - x = 5, which is not equal to zero, you just have to subtract the right hand side of the equation from the left hand side of the equation first.

2y - x = 5

2y - x -5 = 0

In [2]:
x, y = symbols('x y')

eq2 = 2*y - x -5

Substitutions in Equations

Symbols and expressions can be substituted into equations. In the code section below, the variable z is substituted in for the variable x (z replaces x).

In [3]:
x, y, z = symbols('x y z')

eq2 = 2*y - x -5 eq3 = eq2.subs(x,z) eq3

2*y - z - 5