Recursive formula for the sequence 99.4, 0, –99.4, –198.8, where f(1) = 99.4?

(urgent ) use pi 3.14 to estimate the circumference of the circle to the nearest hundredth middle is 4in (urgent )

The sum of two numbers is 86, and their difference is 20. find the two numbers

This is a map of the mars exploration rover opportunity predicted landing site on mars. the scale is 1cm : 9.4km. what are the approximate measures of the actual length and width of the ellipse? i mostly need to know how to set it up : )