input: Write a function to calculate the objective function of a linear equation ax + by = c. The function should take in coefficients a, b, and c and return the result of the objective function.
  def linear_eq(a, b, c, x, y):
      return a*x + b*y - c
  
  # Test cases:
  assert linear_eq(3, 5, 7, 2, 1) == 4
  assert linear_eq(1, 1, 5, 3, 2) == 0
  assert linear_eq(0, 2, 4, 1, 2) == 0
  assert linear_eq(4, 0, 8, 2, 3) == 0
  assert linear_eq(2, 3, 10, 5, 0) == 0
output: def linear_eq(a, b, c, x, y):
      return a*x + b*y - c