Write a cosine function that has an amplitude of 2, a midline of ( y = 4 ), and a period of ( 6/7 ).
a) ( y = 2 cos ( 4π/6/7 x ) )
b) ( y = 2 cos ( 7π/6 x ) + 4 )
c) ( y = 2 cos ( 6π/7 x ) + 4 )
d) ( y = 2 cos ( 7π/6 x ) )