1, if the straight line is a linear function, (m+3)≠0, that is, m≦-3, the intersection with the y axis is above the y axis, and only (2-n) > 0, that is, n y2. 3, (1), because the linear function y decreases with the increase of x when k < 0, so when m-5 < 0, that is, when m < 5, the function y decreases with the increase of x. (2) When the constant term of a linear function is equal to 0, the straight line passes through the origin. So 3-m=0, that is, m=3. (3) If two straight lines ∨ only need k to be equal, then m-5=-2, that is, when m = 3, the straight lines are parallel to y=-2x. (4) If the straight line does not pass through the first quadrant, then k < 0, b < 0, that is, m-5 < 0, 3-n < 0, that is, m < 5, n > 3.