PLEASE HEL MEE An account is opened with $1250 at a bank that pays 4.75% interest yearly, write a function A(t) that tells how much money is in the account after t years

Cos(2θ) = 2cos^2θ - 1, 

 cos^2(θ/2) 
Solving  
cos^2θ = [1 + cos(2θ)]/2. 

replacing θ with θ/2 gives. 
cos^2(θ/2) = (1 + cosθ)/2. 

length of a polar curve of the form r = f(θ) on [a, b] is given by: 
L = ∫ √[r^2 + (dr/dθ)^2] dθ (from θ=a to b). 
hope this helps