# Warm-Up’s.

## Presentation on theme: "Warm-Up’s."— Presentation transcript:

Warm-Up’s

Warm-Up’s 2.

Warm-Up’s

The circumference and Area of a circle

What is the formula relating the circumference to the diameter?

This means APPROXIMATELY EQUAL TO
C = ? x d People knew that the circumference is about 3 times the diameter but they wanted to find out exactly. C ≈ 3 x d This means APPROXIMATELY EQUAL TO

The exact true value is……………
UNKNOWN!!

An approximation to π π≈ forever….

What about the AREA of a circle?
First consider a square The area of this square in terms of r is A= 2r x2r = 4r2 r 2r

What about the AREA of a circle?
Now consider a circle inside the square The area of the circle must be less than the are of the square A < 4r2 2r r 2r Area = ? xr2

Finding a formula for the area of a circle

C= πd or C=2πr Semi-circle=πr πr r

Area of Rectangle= Base x Height
Area = πr x r Area =πr2

The Area and Perimeter of a Circle
A circle is defined by its diameter or radius radius The perimeter or circumference of a circle is the distance around the outside The area of a circle is the space inside it Diameter The ratio of π (pi) π is an irrational number whose value to 15 decimal places is π = We usually say π≈3.14 The circumference is found using the formula C=π d or C= 2πr (since d=2r) The area is found using the formula A=πr2

The Area and Perimeter of a Circle
A circle is defined by its diameter or radius radius The perimeter or circumference of a circle is the distance around the outside The area of a circle is the space inside it Diameter The ratio of π (pi) π is an irrational number whose value to 15 decimal places is π = We usually say π≈3.14 The circumference is found using the formula C=π d or C= 2πr (since d=2r) The area is found using the formula C=πr2

Videos on Circles A Rap about circles