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What is the angle? Right angle Right angle = 90° “ ” is the symbol for a right angle
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perpendicular
What figures are these?
What is the angle?
Right angle
Right angle = 90°
“ ” is the symbol for a right angle
What is the angle?
Acute angle
0°< Acute angle < 90°
What is the angle?
Obtuse angle
90°< Obtuse angle < 180°
What is the angle?
. Straight angle
Straight angle = 180°
What is the angle?
. Round angle
Round angle = 360°
What is this?
Set square
Right angle Right angle side
Right angle side
Right angle
Right angle side
Right angle side
two straight lines are intersecting relations
. intersection point
two straight lines are intersecting relations
two straight lines intersect at right angles
This is the special case of intersection——perpendicular.
when two straight lines intersect at right angles, they are perpendicular to each other.
Right angle Right angle side
Right angle side
In the set square, two right angle sides are perpendicular to each other.
a
bO
Line a and line b intersects at right angle, so line a and line b are perpendicular to each other.
line a is perpendicular to line b, write as: a b⊥ . Or line b is perpendicular to line a, write as: b a⊥ .
( is perpendicular symbol ) ⊥
.O foot of perpendicular
Line c and line d intersects at( ), so line c and line d are ( ).
line c is( )line d, write as( ) Or( )
foot of perpendicular
c
dEE. right angle
perpendicular to each other
perpendicular to c d⊥
line d is perpendicular to line c, write as: d c⊥
nm Is line m and line n
perpendicular to each other?
line m and line n are perpendicular to each other.
A
B
C
D
O
Is line AB and line CD perpendicular to each other?
line AB and CD is just intersect,not perpendicular to each other.
Perpendicular in life
The plumb line is always perpendicular with the horizontal plane. So construction workers use plumb lines to check whether the walls are straight or crooked.
Perpendicular in life
The perpendicular line
on the windscreen will
indicate the glider is
flying direct or not.
Judge
• When two straight lines intersect at 90 °, the two straight lines must be perpendicular to each other. ( )
×
√
intersect at 90 °
• There is only one line perpendicular to line AB. ( )
A B
Judge
• Two adjacent sides of a square are perpendicular to each other. ( )
×
√
adjacent sides of a square
• When two straight lines intersect, the intersection point is called foot of perpendicular. ( )
A
B
C
D
O
intersection point
.
Look at the figure below, which angle is the right angle? Mark with the right angle symbol. Can you find any perpendicular line segments? Write it down
O
A B
CD
A B
CD
O
Thank you!