Question

period of y=-3cos 1/4x

Answer 1

If a function is
\[y=A \cos Bx\ ......(1)\]
the period T is
\[T=\frac{2 \pi}{B}\ ...........(2)\]
In your question B = 1/4. So now you need to plug this value of B into equation (2) to find the period.