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

Prepare your set of compasses 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

REMEMBER TO SHOW ALL OF YOUR CONSTRUCTION LINES 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 8cm 7cm 9cm