**
Criteria of parallelism of straight line and plane:
**

1)
*
If a straight line, lying out of plane, is parallel to
some straight line, lying in the
*

*
plane, then it is parallel to this plane.
*

2)
*
If a straight line and a plane are perpendicular to
the same straight line, then they
*

*
are parallel.
*

*
*

**
Criteria of parallelism of planes:
**

1)
*
If two intersecting straight lines of the same plane
are parallel correspondingly to
*

*
two intersecting straight lines of other plane, then
these planes are parallel.
*

2)
*
If two planes are perpendicular to the same straight
line, then they are parallel.
*

*
*

**
Criteria of perpendicularity of straight line and
plane:
**

1)
*
If a straight line is perpendicular to two interesting
straight lines, lying in a plane,
*

*
then it is perpendicular to this plane.
*

2)
*
If a plane is perpendicular to one of parallel
straight lines, then it is perpendicular
*

*
to the other.
*

**
Straight line inclined to plane.
**
A straight line, intersecting a plane and not perpendicular
to it, is called

*a straight line inclined to plane.*

*
*

**
Theorem about three perpendiculars
**

*. A straight line, that lies in a plane and is perpendicular to a projection of straight line inclined to this plane, is perpendicular to this straight line inclined to plane.*

*
*

**
Criteria of parallelism of straight lines in a space.
**

1)
**
**

*If two straight lines are perpendicular to the same plane, then they are parallel.*

2)
*
If a straight line lies in one of interesting planes
and it is parallel to another plane,
*

*
then it is parallel to line of intersection of these
planes.
*

**
Criterion of perpendicularity of planes:
**

*if a plane goes through a straight line that is perpendicular to another plane, then these planes are perpendicular.*

**
Theorem about common perpendicular to two crossing
straight lines.
**

*Any two*

**crossing straight lines have the only common perpendicular.**
*
*

*
*