Which of the following are identities? Check all that apply. . A. tan2x = 1 + sec2x
. B. sin2x = 1 - cos2x
. C. sin2x- cos?x= 1
0 D. cot2x = csc2x-1

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?