Answer: amplitude \(4\); period \(40^\circ\), or \(\frac{2\pi}{9}\) radians.

The amplitude of a cosine graph \(a\cos bx+c\) is \(|a|\). Here \(a=4\), so the amplitude is

\(4.\)

When the angle is measured in degrees, the period of \(\cos bx\) is \(\frac{360^\circ}{b}\). Here \(b=9\), so

\(\text{period}=\frac{360^\circ}{9}=40^\circ.\)

Equivalently, in radians the period is

\(\frac{2\pi}{9}.\)