Answer: (a)
(i) We have following function:
[tex]f(x)=6\cos (7x)[/tex]For 7x to increase by 2pi, x must increase by following:
[tex]\begin{gathered} 7x=2\pi \\ \\ x=\frac{2\pi}{7} \end{gathered}[/tex]This is the increase in x.
(ii) Period of f(x)
[tex]\begin{gathered} f(x)=\cos (7x) \\ T=\frac{2\pi}{7} \end{gathered}[/tex]This is the period of f(x).
