If the product of two rational numbers is positive, then the sign of the two factors must be positive______ ．

If the product of two rational numbers is positive, then the sign of the two factors must be positive______ ．

∵ the product of two rational numbers is positive, and the sign of the two factors must be the same

Given a = {x 3 ≤ x ＜ 7}, B = {x 2 ＜ x ＜ 10}, find ∁ R (a ∪ b), ∁ R (a ∩ b), (∁ RA) ∩ B, a ∪ (∁ RB)

Set a set of set a = {{X-9 ≤ x \\9 \9 \9 \9 \9 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ ＜ x ≤ 9 or l ≤ x ＜ 17}

What is the sign of a real number

r

Define a kind of operation "*" in real number set R, which has properties: see supplement
(1) for any a, B ∈ R, a * b = b * a; (2) for any a ∈ R, a * 0 = a; (3) for a, B, C ∈ R, (a * b) * C = C * AB + (a * c) + (b * c) - 2C; then what is 1 * 2 = and what is the minimum value of function f (x) = x * 1 / X (x > 0)?

1*2=(1*2)*0=0*1*2+(1*0)+(2*0)-2*0=0+1+2-0=3
F (x) = x * 1 / x = (x * 1 / x) * 0 = 0 * x * 1 / x + X * 0 + 1 / X * 0-2 * 0 = x + 1 / x = [2, positive infinity)