Question 901688
The standard trig form for cos is
y = Acos(Bx+C) + D
we are given 
q(x)=5.3cos(pi(x)/9)
note that C and D are both 0 and pi = 180 degrees, therefore
q(x) = 5.3cos(20x)
the period(T) for sin and cos = (2*pi) / B 
B = 20 and pi = 180
T = (2 * 180) / 20 = 18