Circles

Question 1

Circumference=

Answer 1

pi x diameter or 2pi x radius

Question 2

Area=

Answer 2

pi r^2

Question 3

Radius=

Answer 3

√Area/pi

Question 4

Arc length=

Answer 4

Angle/360 x 2pi x r

Question 5

Area of sector=

Answer 5

Angle/360 x pi x r^2

Question 6

Circle Theorem 1

Answer 6

Every angle subtended at the circumference of a semi-circle by the diameter is a right angle

Question 7

Circle Theorem 2

Answer 7

The angle at the centre is twice the angle at the circumference when they are both subtended by the same arc

Question 8

Cirlce Theorem 3

Answer 8

In a cyclic quadrilateral the opposite angles sum to 180

Question 9

Circle Theorem 4

Answer 9

Angles in the same segment are equal

Question 9

Circle Theorem 5

Answer 9

The tangent at any point on a circle is perpendicular to the radius at that point

Question 10

Circle Theorem 6

Answer 10

Tangents from an external point are equal in length

Question 11

Circle Theorem 7

Answer 11

The angle between a tangent and a chord is equal to the angle in the alternate segment

Question 12

Circle Theorem 8

Answer 12

A radius bisects a chord at 90 degrees