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. Return the value of ax + by - c.
  
  def linear_eq(a, b, c, x, y):
      return a*x + b*y - c
  
  assert linear_eq(3, 5, 7, 1, 2) == 0
  assert linear_eq(2, 4, 6, 2, 1) == 0
  assert linear_eq(4, 7, 10, 1, 1) == 1
  assert linear_eq(1, 1, 1, 0, 0) == -1
  assert linear_eq(0, 0, 0, 5, 5) == 0
output: def linear_eq(a, b, c, x, y):
      return a*x + b*y - c