input: Write a function to calculate the objective function of a linear equation of the form ax + by = c. Given the coefficients a, b, and c, the function should return the value of the equation.
  
  def linear_eq(a, b, c, x, y):
      return a*x + b*y - c
  
  # Test cases:
  assert linear_eq(3, 5, 7, 1, 1) == 1
  assert linear_eq(3, 5, 7, 2, 2) == 3
  assert linear_eq(3, 5, 7, 0, 0) == -7
  assert linear_eq(3, 5, 7, 1, 0) == -4
  assert linear_eq(3, 5, 7, 0, 1) == -2
output: def linear_eq(a, b, c, x, y):
      return a*x + b*y - c