Consider the equation of a circle x^{2} -2x + y^{2} - 4y - 4 = 0 if the line 2x - y + a = 0 is its diameter. then find the value of a?

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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?

Is the point (0, 8) on the x-axis or y-axis? how do you know?