Derive the equation of the parabola with a focus at (0, 1) and a directrix of y = −1. f(x) = −one fourth x^2
f(x) = one fourth x^2
f(x) = −4x^2
f(x) = 4x^2

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?