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!