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Formulas from plane analytic geometry

DISTANCE d BETWEEN TWO POINTS P1(x1,y1) AND P2(x2,y2)

SLOPE m OF LINE JOINING TWO POINTS P1(x1,y1) AND
P2(x2,y2)

EQUATION OF LINE JOINING TWO POINTS P1(x1,y1) AND
P2(x2,y2)

y = mx + b

where is the intercept on the y axis, i.e. the y intercept.

EQUATION OF LINE IN TERMS OF x INTERCEPT a≠0 AND y INTERCEPT b≠O

NORMAL FORM FOR EQUATION OF LINE

xcosα + ysinα = p

where p = perpendicular distance from origin O to line

and          α = angle of inclination of perpendicular with

positive x axis.

GENERAL EQUATION OF LINE

Ax + By + C = 0

DISTANCE FROM POINT (x1, y1) TO LINE Ax + By + C = 0

where the sign is chosen so that the distance is nonnegative.

ANGLE ψ BETWEEN TWO LINES HAVING SLOPES m1, AND m2

Lines are parallel or coincident if and only if mx = m2.

Lines are perpendicular if and only if m2 = -1/m1.

AREA OF TRIANGLE WITH VERTICES AT (x1, y1), (x2, y2), (x3, y3)

Area

= ± ½ (x1y2 + y1x3 + y3x2 - y2x3 - y1x2 - x1y3)

where the sign is chosen so that the area is nonnegative. If the area is zero the points all lie on a line.

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