Drawing Angles

Slideshow 41, MathematicsMr Richard SasakiRoom 307

OBJECTIVES• Understand how to draw 90o and 60o angles

• Understand how to bisect and add to these to make other angles (such as 30o and 120o)

90O ANGLESo far, we have constructed some shapes and bisected lines and angles. Today we will draw some angles. We already know how to draw a 90o angle so today we will use a slightly different method. (There are quite a few different ways to do this.)

90O ANGLEDraw and label a right-angle with line segments of any length starting at vertex A.

Label a point D somewhere above and close to the line segment.

Make distance AD the radius of the compass.

90O ANGLENext, draw an arc from D that passes through the line segment, point A and above point A again.

Draw a line segment from the new crossing made, through D and then up to the point above A.

Draw a line segment from A to the point above it…And finally, remove the line passing through D!Don’t forget to label it!

Try Q1 – 4!

ANSWERS

A

270𝑜

45𝑜O

A

B

135𝑜

60O ANGLE60o is easy! Let’s draw it as for line segments and .

Measure the compass just over half and draw a large arc from P covering where may go.

From the point made, draw a mark over the arc and then join this mark to point P.

Finally connect P to this and label it and label the angle!

R

60o

30O ANGLEYou can just simply cut the 60o angle in half, but there is a quicker way!

Measure the compass just over half of a segment again and draw an arc in the same place and name the crossing S.

Place the point at S and cross the arc.

Make a point T.

30O ANGLEPlace the point at T and cross over the new point. Label this point R.

Finally, draw a line segment and label the angle.

30o

Try Q5 – 9!

ANSWERSQ

P R60𝑜

120𝑜Q

P R

AB30𝑜

C

AB C15𝑜

X

Y Z75𝑜