Reversals of the Earth's magnetic polarity

Scientists understand that Earth's magnetic field has flipped its polarity many times over the millennia. ... Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 to 300,000 years, although it has been more than twice that long since the last reversal.

reflecting point a across the origin negates both of its coordinates.

b = (5, -4)