I am trying to solve an equation with multiple variables for b

Question

I am trying to solve a simple equation, but this is what is being outputted:

the equation is y = m*x + b,

y, m, and b are already defined

I would like to print b.

import sympy
while True:
    x1 = int(input('x1: '))
    y1 = int(input('y1: '))

    x2 = int(input('x1: '))
    y2 = int(input('y1: '))

    m = (y1-y2) / (x1-x2)
    print(m)
    
    m = sympy.symbols('m')
    x = sympy.symbols('x')
    y = sympy.symbols('y')
    b = sympy.symbols('b')
    
    a = y, x*m + b
    
    print(sympy.solve(a, b))

Select all lines and press tab after `while True` – cyborg Dec 31 '21 at 09:59 — cyborg, Dec 31 '21 at 09:59

score 0 · Accepted Answer · answered Dec 31 '21 at 09:56

You can try like:

import sympy
# while True:
x1 = int(input('x1: '))
y1 = int(input('y1: '))

x2 = int(input('x1: '))
y2 = int(input('y1: '))

m = (y1-y2) / (x1-x2)
print(f"m: {m}")

b = sympy.symbols('b')

a = y, x*m + b

print(sympy.solve(y1 -x1*m - b, b))

Test:

x1: 1
y1: 7
x1: 2
y1: 12
m: 5.0
# out: [2.00000000000000]

score 0 · Answer 2 · answered Dec 31 '21 at 16:54

We need to give two equations to sympy, one for each x,y combination. First, create the general line equation a = Eq(y, x*m + b). And then substitute the individual values for x and for y to find the two equations.

import sympy

x1, y1 = 1, 4
x2, y2 = 5, 8

x, y, m, b = sympy.symbols('x y m b')

a = sympy.Eq(y, x * m + b)
eq1 = a.subs({x: x1, y: y1})  # Eq(4, b + m)
eq2 = a.subs({x: x2, y: y2})  # Eq(8, b + 5*m)
print(sympy.solve([eq1, eq2], (m, b)))  # {m: 1, b: 3}

I am trying to solve an equation with multiple variables for b

2 Answers2