Calculate the effective gravitational field vector g at Earth's surface at the poles and the equator. Take account of the difference in the equatorial (6378 km) and polar (6357 km) radius as well as the centrifugal force. How well does the result agree with the difference calculated with the result g=9.780356[1+0.0052885sin2λ−0.0000059sin2(2λ)]m/s2 where λ is the latitude?