Question

Indicate the two quadrants "theta" could terminate in if:
1. sin theta = 3/5
2. cos theta = -0.45
how can you know this, memorize in an easy way?

Answer 1

sin can be positive in 1st and 2nd quadrants.
cos can be negative in 2rd and 3rd quadrants.

You don't need to memorize. Take a look at it below. When will sin and cos be negative? Becomes clear once you know which quadrants x and y are negative.