Bisecting an angle

Bisecting an angle

Draw an acute angle

How can we accurately bisect this angle without the use of a ruler or

protractor ?

Prepare your set of compasses by lining the tip up with the point of your pencil

Adjust the compasses to a setting that is smaller than the length of the

lines that create the angle

Draw an arc across each length of the angle.

Place the compasses on the point where one arc crosses a length and

draw a second arc

Without changing the compasses setting repeat for the other length so

that the two arcs cross.

Line a straightedge or ruler from the point of the angle to the point where the

arcs cross

Draw a line that runs from the point of the angle and through the point where

the arcs cross

Do NOT rub out your construction lines

Check your construction by measuring each of the angles created

Draw an obtuse angle

Prepare your set of compasses

Adjust the compasses to a setting that is smaller than the length of the

lines that create the angle

Draw an arc across each length of the angle.

Place the compass on the point where one arc crosses a length and

draw a second arc

Without changing the compass setting repeat for the other length so

that the two arcs cross.

Line a straightedge or ruler from the point of the angle to the point where the

arcs cross

Draw a line that runs from the point of the angle and through the point where

the arcs cross

Do NOT rub out your construction lines

Check your construction by measuring each of the angles created

Your turn

Draw 5 angles in your book and bisect each one making sure you clearly show

ALL of your construction lines

Perpendicular bisect of a line

Draw a line 6cm long

Prepare your set of compasses and open them to just over half the length

of the line

Place the point of the compasses on one end of the line and draw an arc above the

line and another below the line.

BE CAREFUL NOT TO LET THE COMPASSES MOVE

Place the point of the compasses on the other end of the line and draw the arcs

again

Line a straightedge or ruler up with the meeting points of the two sets of arcs

Draw a line that runs through each of the meeting points of the arcs

Do NOT rub out your construction lines

Check your construction by measuring one of the angles where the two lines

cross

Draw a line 5cm long

Prepare your set of compasses and open them to just over half the length

of the line

Place the point of the compasses on one end of the line and draw an arc above the

line and another below the line.

BE CAREFUL NOT TO LET THE COMPASSES MOVE

Place the point of the compasses on the other end of the line and draw the arcs

again

Line a straightedge or ruler up with the meeting points of the two sets of arcs

Draw a line that runs through each of the meeting points of the arcs

Do NOT rub out your construction lines

Check your construction by measuring one of the angles where the two lines

cross

Your turn

Accurately draw each of the lines in your books and create a perpendicular

bisector for each one

REMEMBER TO SHOW ALL OF YOUR CONSTRUCTION LINES

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