Answer:
7.
I) must be true
II) 1 - 1 < 2 - 4 --> false
III) (-10)*(-10) < 1*1 --> false
IV) 1/2 < 2/10 --> false
So (B) 1 must be true
8.
x!·(x + 1)!/2 = (x + 1)!^2 / (2·(x + 1)) = (17 + 1)!^2 / (2·(17 + 1)) = 18!^2 / 6^2
(D)
9.
2·√3·6 = √((2·√3)^2 + 6^2)·h --> h = 3 --> (C)
