Please help me with this math

Find the value of the cosine for angle a

Do some research and find a city that has experienced population growth. determine its population on january 1st of a certain year. write an exponential function to represent the city’s population, y, based on the number of years that pass, x after a period of exponential growth. describe the variables and numbers that you used in your equation.

Which expression is rational? 6. , square root two, square root 14, square root 49