1, point oblique type: a point (x0, y0) on a straight line is known, and the slope k of the straight line exists, then the straight line can be expressed as: y-y0 = k (x-x0); When k does not exist, the straight line can be expressed as: x = x0 2, oblique type: y = kx+b (k. When k < 0, y decreases with the increase of x, and when two straight lines are parallel, K 1=K2. When two straight lines are perpendicular, K 1 X K2 =-1 3, and the two-point formula: x 1 is not equal to x2, and y 1 is not equal to y2. Note: Limitations of various linear equations: (1) The formula of point inclination and the formula of inclined section cannot be expressed. (2) Two-point formula cannot represent a straight line parallel to the coordinate axis; (3) Intercept formula cannot represent a straight line parallel to the coordinate axis or passing through the origin; (4) The coefficients A and B in the general formula of linear equation cannot be zero at the same time. (Y-Y 1)/(Y2-Y 1)=(X-X 1)/(X2-X 1)