Question

question about verifying if a function has an inverse (picture included)

Answer 1

my first instinct was to visualize a graph and in my head clearly it doesn't pass the horizontal line test. But looking at the answer key, it says that it is a 1-1 function. WHY?

Answer 2

Teachers say it has an inverse if it is always increase or always decreasing (we can check by looking at the derivative and plugging in sample points around the critical #) this answer seems to contradict everything i have learned...