Answer:
5
Step-by-step explanation:
I'm assuming you want to find the maximum value of y
recall that for any cosine function y = A cos ( g(x) ), where g(x) is any arbitrary function, that A represents the amplitude of the cosine function.
By definition, the amplitude is the maximum the value which the cosine term can take.
hence for your expression:
y= -1 + 6 cos ( 2π/7(x-5) )
max value of y = -1 + (max value of cosine function)
max value of y = -1 + (amplitude of cosine function)
max value of y = -1 + 6 = 5
