Note: 1. Midpoint coordinate formula:
If there are two points A(x 1, y 1) B(x2, y2), the coordinates of their midpoint p are ((x 1+x2)/2, (y 1+y2)/2.
2. Linear equation:
1) general formula: applicable to all straight lines.
Ax+By+C=0 (where a and b are not 0 at the same time)
2) Point skew: a point (x0, y0) on a straight line is known and the slope k of the straight line exists. The straight line can be expressed as
y-y0=k(x-x0)
When k does not exist, a straight line can be expressed as
x=x0
(3) The formula of tangent moment: it is not applicable to the straight line perpendicular to any coordinate axis and the straight line passing through the origin.
Given that a straight line intersects the X axis at (a, 0) and the Y axis at (0, b), it can be expressed as
x/a+y/b= 1
The oblique equation is y = kx+b.
When two straight lines are parallel, K 1=K2.
When two lines are perpendicular, K 1 X K2 =-1.
(4) Two-point type
(y-y1)/(y2-y1) = (x-x1)/(x2-x1) x1is not equal to x2 y 1 is not equal to y2.
(5) point-to-line equation
| ax+by+c |/sqr (a 2+b 2) sqr is the root number and 2 is the square.
Note: the limitations of various forms of linear equations:
(1) point inclination and inclination cannot represent a straight line without slope;
(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.