(a)
Write down the mathematical name for this solid.
(b)
(i) Measure the size of angle x.
(ii) Write down the mathematical name for this type of angle.
(c)
Points A, B and C lie on the circle, centre O.
AB = 11 cm and BC = 5 cm.
(i) Give a geometrical reason why angle ACB is 90°.
(ii) Calculate the circumference of the circle.
(iii) Show that AC is 9.8 cm, correct to 2 significant figures.
(d) The surface area of a sphere is 250 cm². Calculate the radius of the sphere.
[The surface area, A, of a sphere with radius r is \( A = 4\Pi r^{2}\)]
▶️ Answer/Explanation
(a) Ans: Cylinder
(b)(i) Ans: 137° (accept 136-138°)
(b)(ii) Ans: Obtuse angle
(c)(i) Ans: Angle in a semicircle is 90°
(c)(ii) Ans: 34.6 cm (using π = 3.142)
Calculation: Circumference = π × diameter = 3.142 × 11 ≈ 34.6 cm
(c)(iii) Ans: Using Pythagoras: √(11² – 5²) = √96 ≈ 9.8 cm
(d) Ans: 4.46 cm
Calculation: Using A = 4πr² → r = √(250/(4π)) ≈ 4.46 cm
(a) The diagram shows a circle.
(i) The diameter of this circle is 168 mm. Write down the radius of this circle.
(ii) On the diagram, draw a chord of this circle.
(b) The scale drawing shows the position of ship A and the position of ship B.
The scale is 1 cm represents 6 km.
Another ship, C, is 45 km from ship B on a bearing of 124°.
(i) On the scale drawing, mark the position of ship C.
(ii) Find the actual distance of ship C from ship A.
(c) (i) Show that the interior angle of a regular octagon is 135°.
(ii)
Show that two regular octagons and a square meet at a point without any gaps.
(d)
The diagram shows points D, E and F on the circumference of a circle.
DF is a diameter of the circle.
Find angle EDF.
▶️ Answer/Explanation
(a)(i) Ans: 84 mm
Radius = Diameter/2 = 168/2 = 84 mm
(a)(ii) Ans: Any straight line connecting two points on the circumference
A chord is any line segment whose endpoints lie on the circle.
(b)(i) Ans: Position marked 7.5 cm from B at 124°
45 km ÷ 6 km/cm = 7.5 cm. Measure 124° from north line at B.
(b)(ii) Ans: 57 km
Measure distance on diagram (about 9.5 cm) and multiply by 6.
(c)(i) Ans: Proof shown
Interior angle = (n-2)×180°/n = (8-2)×180°/8 = 135°
(c)(ii) Ans: Proof shown
135° (octagon) + 135° (octagon) + 90° (square) = 360° which fits perfectly.
(d) Ans: 41°
Angle in semicircle is 90°, so angle EDF = 180° – 90° – 49° = 41°.