Answer:
[tex]y = 2 \cos(4x) - 1 \\ when \: y = 0 \\ \cos(4x) = \frac{1}{2} \\ 4x = 60 \\ x = 15 \\ when \: x = 0 \\ y = 2 - 1 = 1 \\ intercepts = > (15, \: 0) \: and \: (0, \: 1) \\ midpoints : ( \frac{15 + 0}{2} , \: \frac{0 + 1}{2} ) \\ = (7.5, \: 0.5) \\ gradient = \frac{1 - 0}{0 - 15} \\ = - \frac{1}{15} \\ y = mx + c \\ at \: (7.5, \: 0.5) \\ 0.5 = - \frac{1}{15} \times 7.5 + c \\ 0.5 = - 0.5 + c \\ c = 1 \\ \therefore \: y = - \frac{1}{15} x + 1 \\ = > 15y = - x + 15[/tex]
