Name __ Gr. Lesson 4.1 – Circles Jan. Objective: to measure radius and diameter and discover their relationship

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__Objective: to measure radius and diameter and discover their relationship.

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__Objective: to measure radius and diameter and discover their relationship.All points in a circle are the same distance from the centre. This distance is called the radius.Radius – the distance from the centre of a circle to the outside of the circle.

radius

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__Objective: to measure radius and diameter and discover their relationship.All points in a circle are the same distance from the centre. This distance is called the radius.Radius – the distance from the centre of a circle to the outside of the circle.The longest line segment in any circle is the diameter. It always passes through the centre.Diameter – the distance across a circle directly Through the centre.

radius

diameter

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__All points in a circle are the same distance from the centre. This distance is called the radius.Radius – the distance from the centre of a circle to the outside of the circle.The longest line segment in any circle is the diameter. It always passes through the centre.Diameter – the distance across a circle directly Through the centre.The radius is always ½ the diameter & the diameter is always 2 times the radius.d = diameter & r = radiusSo, r = d /2 and d = 2 x r or d = 2r.

radius

diameter

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__What can you say about a circle with a radius of 5cm. and a circle with a diameter of 10 cm.?


Radi

us =

5cm


Both circles are exactly the same! They are __________?

Radi

us =

5cm

Diam

eter

= 1

0cm


Both circles are exactly the same! They are congruent!

Radi

us =

5cm

Diam

eter

= 1

0cm

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__PRACTICE: Page 132 #’s 2,3,4,6

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__PRACTICE: Page 132 #’s 2,3,4,6

#2 - Draw a circle with each radius without using a compass.a) 7 cm b) 4 cmLabel the radius, then find the diameter.Explain the method you used to draw the circles.What are the disadvantages of not using a compass?

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__PRACTICE: Page 132 #’s 2,3,4,6#2 - Draw a circle with each radius without using a compass.a) 7 cm b) 4 cmLabel the radius, then find the diameter.Explain the method you used to draw the circles.What are the disadvantages of not using a compass?

7 cm.


d = 2r, so d = 2 x 7cm = 14cm.

7 cm.


d = 2r, so d = 2 x 7cm = 14cm.

7 cm.

4 cm.


d = 2r, so d = 2 x 4cm = 8cm.

d = 2r, so d = 2 x 7cm = 14cm.

7 cm.

4 cm.


d = 2r, so d = 2 x 4cm = 8cm.

d = 2r, so d = 2 x 7cm = 14cm.To draw the circles, I made a horizontal and verical diameter. Then arced from each point. If you don’t use a compass you are not as accurate.

7 cm.

4 cm.

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__PRACTICE: Page 132 #’s 2,3,4,63. a) A circle has diameter 3.8 cm. What is the radius?

b) A circle has radius 7.5 cm. What is the diameter?

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__PRACTICE: Page 132 #’s 2,3,4,63. a) A circle has diameter 3.8 cm. What is the radius?r = d /2, So r = 3.8 cm / 2 = 1.9cm

b) A circle has radius 7.5 cm. What is the diameter?

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__PRACTICE: Page 132 #’s 2,3,4,63. a) A circle has diameter 3.8 cm. What is the radius?r = d /2, So r = 3.8 cm / 2 = 1.9cm

b) A circle has radius 7.5 cm. What is the diameter?d = 2r, So d = 7.5cm x 2 = 15cm

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__

PRACTICE: Page 132 #’s 2,3,4,6 #4) A circular tabletop is to be cut from a rectangular pieceof wood that measures 1.20 m by 1.80 m.What is the radius of the largest tabletop that could be cut?Justify your answer. Include a sketch.

1.80m

1.20m


PRACTICE: Page 132 #’s 2,3,4,6#4) A circular tabletop is to be cut from a rectangular pieceof wood that measures 1.20 m by 1.80 m.What is the radius of the largest tabletop that could be cut?Justify your answer. Include a sketch.

The largest circle that can fit in this rectangle has a diameter of the smaller width = 1.20m.

1.80m

1.20m


PRACTICE: Page 132 #’s 2,3,4,6#4) A circular tabletop is to be cut from a rectangular pieceof wood that measures 1.20 m by 1.80 m.What is the radius of the largest tabletop that could be cut?Justify your answer. Include a sketch.

The largest circle that can fit in this rectangle has a diameter of the smaller width = 1.20m.So… the radius is 1.20 / 2 = 0.6m

1.80m

1.20m0.6m


PRACTICE: Page 132 #’s 2,3,4,66) A glass has a circular base with radius 3.5 cm.A rectangular tray has dimensions 40 cm by 25 cm.How many glasses will fit on the tray?



40cm

25cm

3.5cm



Diameter = 2r = 2 X 3.5 = 7cm

So, how many 7’s in 40? And how many 7’s in 20?

3.5cm

25cm

40cm



Diameter = 2r = 2 X 3.5 = 7cm

So, how many 7’s in 40? And how many 7’s in 20? 5 glasses along the length & 3 glasses along the width, so

5 X 3 = 15 glasses!

3.5cm

25cm

40cm

Documents

Name ______ Gr.__ Lesson 4.1 – Circles Jan.__ Objective: to measure radius and diameter and discover their relationship

Name __ Gr. Lesson 4.1 – Circles Jan. Objective: to measure radius and diameter and discover their relationship