The fourth through the seventh terms of an arithmetic sequence are given by a4 = 17, a5 = 21, a6 = 25, and a7 = 29. Which formula can be used to find an?

A. an= 17+4(n-1)
B. an= 9+4(n+1)
C. an= 5+4(n-1)
D. an= 5+4(n+1)
E. an= 4+5(n-1)

There is a line with slope 1/a going through the point (a, a²). find the equation of the line perpendicular to this line at this point. (don’t let this problem intimidate you! solve the problem as you would if i’d given you specific values. just use variables instead.)

Alake near the arctic circle is covered by a 222-meter-thick sheet of ice during the cold winter months. when spring arrives, the warm air gradually melts the ice, causing its thickness to decrease at a constant rate. after 333 weeks, the sheet is only 1.251.251, point, 25 meters thick. let s(t)s(t)s, left parenthesis, t, right parenthesis denote the ice sheet's thickness sss (measured in meters) as a function of time ttt (measured in weeks).

Select all the correct answers. what is 221,000,000,000,000,000,000 expressed in scientific notation?