The coordinates of the intersection point are ((3m-6)/(m 2+3), (4m+6)/(m 2+3)), (/is the divisor, and m 2 stands for the square of m). Because the coordinates of the intersection point are in the second quadrant, the abscissa is less than zero and the ordinate is greater than zero, and because m 2+3 is always greater than zero. 0,4m+6 > 0 is enough, and the solution is-3/2 < m <; 2, which is the range of m.
2. Suppose the stall owner buys X newspapers from the newspaper office every day, and the monthly profit is Y yuan, so it is 250×400, and Y = 0.3××× 20+0.3× 250×10+0.05× (x-250 )×10-0.2.
∫ The function f(x) monotonically increases on [250,400]. When x=400, the maximum y =825, that is, the stall owner can get the maximum profit by buying 400 newspapers from the newspaper office every day, and the maximum profit is 825 yuan.
20.A={x R }={x }，B={x R }={x }
∵ One, ∴ Get one