Three Dimensional Geometry
Three Dimensional Geometry PDF Notes, Important Questions and Synopsis
SYNOPSIS
 3D geometry is a threedimensional geometry where each point is described in threedimensional space with three coordinate axes named X, Y and Z.

Section Formula:
If c is the point which divides a line PQ in the ratio m:n, then the coordinates of c are given by
c =" > 
Direction Cosines:
The angles α, β and γ made by the directed line L passing through the origin with x, y and z axes respectively are called direction angles.
Cosines of these angles (cos α, cos β and cos γ) are called the direction cosines of line L.
Note: The direction cosines of the directed line not passing through the origin can be obtained by drawing a line parallel to it which passes through the origin. 
Direction Ratios:
If l, m and n are the cosines of the vector and a, b and c are three numbers such that they are proportional to l, m and n respectively, then a, b and c are called the direction ratios of the vector .
Also, 
For points P(x_{1}, y_{1,} z_{1}) and Q(x_{2}, y_{2}, z_{2}), the direction ratios of line PQ are
" >. 
A line is uniquely determined if it passes through
 a given point and parallel to a vector/line having direction cosines
 the two given points
 Two lines having direction cosines l_{1}, m_{1}, n_{1} and l_{2}, m_{2}, n_{2} are
 Perpendicular if and only if l_{1} l_{2} + m_{1} m_{2} + n_{1} n_{2} = 0
 Parallel if
 Two lines having direction ratios a_{1}, b_{1}, c_{1} and a_{2}, b_{2}, c_{2} are
 Perpendicular if and only if a_{1} a_{2} + b_{1} b_{2} + c_{1} c_{2} = 0
 Parallel if
 If two lines intersect at a point, then the shortest distance between them is zero.
 If two lines are parallel, then the shortest distance between them is the perpendicular distance.
 Two lines which are neither parallel nor intersect are called skew lines.
These lines are noncoplanar, i.e. they do not belong to the same 2D plane.  Angle between two skew lines:
Angle between two skew lines is the angle between two lines which are drawn from any point and parallel to each of the skew lines.  A normal vector, simply called normal, is a vector perpendicular to a surface.
 Plane:
A plane is a surface such that a line joining any two points taken on it lies completely on the surface.
A plane is uniquely determined if The normal to the plane and its distance from the origin is given.
 It passes through a point and perpendicular to a given direction.
 It passes through three given noncollinear points.
Note: A line containing three collinear points can be a part of many planes.
 Angle between two planes is the angle between their normals.
 Planes a_{1}x + b_{1}y + c_{1}z + d_{2} = 0 and a_{2}x + b_{2}y + c_{2}z +d_{2} = 0 are
 Perpendicular if a_{1}a_{2} + b_{1}b_{2} + c_{1}c_{2} = 0
 Parallel if
 The angle between a line and a plane is the complement of the angle between a line and the normal to the plane.
 Distance of a point from a plane is the length of the line (perpendicular to the plane) from the plane to the point.
Related Chapters
 Sets, Relations and Functions
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 Matrices and Determinants
 Permutations and Combinations
 Mathematical Induction
 Binomial Theorem and its Simple Applications
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 Limit, Continuity and Differentiability
 Integral Calculus
 Differential Equations
 Coordinate Geometry
 Vector Algebra
 Statistics and Probability
 Trigonometry
 Mathematical Reasoning