A research team is testing a product that will minimize wrinkles among older adults. Volunteers in the age group of 40 to 45 are included in the research. The research team gives a cream to be applied on the face to one group and a placebo cream to the other group.

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 a. at what time does the particle reverse direction? b. when is the displacement positive? (round one decimal place and answer in interval notation) c. when is the displacement negative? (round one decimal place and answer in interval notation) d. when is the particle’s acceleration positive? (round one decimal place and answer in interval notation) e. when is the particle’s acceleration negative? (round one decimal place and answer in interval notation)