Gavin is looking at stars with his farther and notices some of the stars are brighter than others. Gavin's father tells him that the brightness of a star is one way that scientists determine the star's magnitude. What other property, which Gavin and his father might observe, is used by scientists to classify stars?
A. The constellation the star is in
B. The gas that makes up the star
C. The star's rotation
D. The star's color

The position of a moving particle is given by the position function: f(t)=-9t-t^2-0.2t^3+0.1t^4 0 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)