Prove that the coordinate (a, b) (b, a) are inverses of one another.

The parabola x = y² - 9 opens: a.)up b.)down c.) right d.)left

Each person in an it department of 25 people works on at least one of 3 major projects: system security, program implementation, platform development. 10 people work on system security, 13 work on program implementation, and 12 work on platform development. 4 people work on system security and platform development, 5 people work on program implementation and platform development, and 2 people work on all three projects. how many people work on system security and program implementation?

Plz hurry evaluate the expression a+b where a=8 and b=19