Need some clarification on an answer. The question is (TCO 3) Give the specific form of the equation by evaluating a, b, c through an inspection of...

The question is

My answer is:

a is the amplitude of the wave and it is the distance from the center to the peak of the wave. It is equal to 5

b is given by 2 π divide by the period of the wave. In the above case, the period is 15 b = 2 π/15

c is given by displacement multiply by b. the displacement is 10 and b = 2 π/15

10× 2π/15 = 4π/3

Therefore, y=5sin (2π/15x + 4π/3)

However my professor say the answer is only half correct. What am I missing?

The text book says