Page 292 - ICSE Math 6

Mental Maths 3. (a) 13 triangles (b) 14 squares
1. (a) False (b) True (c) True (d) False (e) True 4. (a) Isosceles (b) Scalene (c) Equilateral
2. (a) 2 (b) 45° (c) 40° (d) same 5. (a) Acute-angled (b) Obtuse-angled (c) Right-angled
Practice Time 6. 88 tiles 7. A and D; B and C
8. 90° 9. By bisecting an angle of 60°. 10. Namibia Think Smart

Think Smart 1. Into two right triangles.
1. No; 45° 2. Rectangle (or square) 2. (a) True, as all angles are of 60°.
(b) False, as an isosceles triangle can also be right-angled
Chapter 17 or acute-angled.
Exercise 17.1 (c) True, as the sides other than hypotenuse can be of
1. (a) Isosceles (b) Scalene (c) Equilateral equal length.
2. (a) Acute-angled (b) Obtuse-angled (d) True, as the sides other than hypotenuse can be of
different length.
(c) Right-angled (e) False, as a scalene triangle can also be right-angled
3. (a) Equilateral and acute-angled or acute-angled.
(b) Scalene and right-angled 3. All the medians and altitudes of an equilateral triangle are
(c) Scalene and obtuse-angled equal. The median and altitude of an isosceles triangle
(d) Scalene and acute-angled passing through the vertex where its equal sides meets
are equal.
(e) Isosceles and acute-angled 4. (a) Top of a die; Chess board (b) Wall; Blackboard
(f) Isosceles and obtuse-angled (Answers may vary)
4. (a) 60° (b) 50° (c) 115° (d) 80°
5. Floor is a rectangle in shape.
Exercise 17.2
1. (a) True (b) False (c) False Chapter 18
2. (a) A rectangle having all sides equal is a square. Exercise 18.1
(b) A parallelogram with a right angle becomes a rectangle. 1. (a) O (b) SR (c) AB (d) OA; OB; OP (e) P
(c) A rhombus with a right angle becomes a square. 2. 12 cm 3. (a) 3 cm (b) sector (c) segment
(d) O; Q (e) exterior
(d) The opposite sides of a square are parallel, so it is a 4. (a) 2r (b) 2r 5. (a) exterior (b) interior
parallelogram.
6. 4.5 cm 7. 5 cm
3. ; Yes, (Answers may vary) Mental Maths
1. (a) False (b) True (c) False (d) False (e) True
4. 180° 5. 0° 6. 5 cm 7. 15 cm; 27 cm (f) False (g) False
Mental Maths 2. (a) CD (b) DI or EF (c) AOB (d) GH 3. 4
1. (a) True (b) True (c) False (d) False (e) True Practice Time
(f) False (g) True (h) True 1. 16 cm
2. (a) pentagon (b) sides; angles (c) polygon 2. (a) in the interior (b) in the exterior
(d) triangle (e) 4 (f) perpendicular (g) trapezium (c) on the circumference
(h) an isosceles (i) an equilateral (j) a scalene 3. 9 cm 4. 6 cm 9. 90° 12. 5 13. 23 m
(k) centroid Think Smart
1. (a) True, as the centre of a circle lies in its interior.
Practice Time (b) True, as the diameter of circle A lies in the interior
1. A trapezium is a quadrilateral with a pair of parallel sides. of circle B.
A parallelogram is a quadrilateral with two pairs of parallel (c) False, as the points in the exterior of circle B also
sides. lie in the exterior of circle A.
A rectangle is a parallelogram in which each angle is a (d) False, as each secant of circle A will intersect circle
right angle. B at two points.
2. A simple closed figure made up of line segments only (e) True, as each tangent of circle A will intersect circle
is called a polygon. Square, rhombus and rectangle are B at two points.
three polygons having four sides. 2. (c)

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