Happy holidays! please help me, it's algebra 2!

What are “like terms”? why can we only add like terms?

In triangle opq right angled at p op=7cm, oq-pq=1 determine the values of sinq and cosq

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)