🎬 Understanding quadrilaterals · Class 8 maths · 3:32
Understanding quadrilaterals: Class 8 maths video
Master Class 8 quadrilaterals with Captain Calc! Learn polygon angle sums, parallelogram properties, rhombuses, rectangles, and squares through fun math missions.
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0:00 Class 8 maths. Understanding quadrilaterals.
0:04 Greetings, hero!
0:06 Captain Calc here to help you unlock the power of four-sided shapes called quadrilaterals.
0:12 Polygons and Interior Angle Sum.
0:15 A polygon is a closed flat shape made of straight line segments.
0:20 A polygon with 4 sides is called a quadrilateral.
0:24 Try this one. Three angles of a quadrilateral are 70°, 100°, and 80°. Find the fourth angle.
0:35 Add the given three angles: 70° + 100° + 80° = 250°.
0:44 Subtract from total interior sum 360°: 360° - 250° = 110°.
0:57 So the answer is 110°.
1:00 Exterior Angles of Polygons.
1:03 An exterior angle is formed between one side of a polygon and the extension of its adjacent side.
1:10 The sum of the exterior angles of any convex polygon is always equal to 360°.
1:18 Try this one. Find each exterior angle of a regular polygon with 8 sides.
1:26 Use the formula: Each exterior angle = 360° ÷ n.
1:33 Divide 360° by 8: 360° ÷ 8 = 45°.
1:42 So the answer is 45°.
1:45 Properties of Parallelograms.
1:48 A parallelogram is a quadrilateral where both pairs of opposite sides are parallel.
1:54 In any parallelogram, opposite sides are equal in length and opposite angles are equal in measure.
2:01 Try this one. In parallelogram ABCD, angle A = 70°. Find the measures of angle B and angle C.
2:11 Opposite angles are equal, so angle C = angle A = 70°.
2:18 Adjacent angles add up to 180°, so angle B = 180° - 70° = 110°.
2:30 So the answer is angle B = 110°, angle C = 70°.
2:37 Special Parallelograms: Rhombus, Rectangle, and Square.
2:42 A rectangle is a parallelogram with four right angles.
2:46 Its diagonals are equal in length.
2:49 Try this one. A rhombus has side length 8 cm. What is its perimeter?
2:56 All 4 sides of a rhombus are equal.
2:59 Perimeter = 4 × side = 4 × 8 = 32 cm.
3:06 So the answer is 32 cm.
3:08 Your turn. Three angles of a quadrilateral are 50°, 110°, and 120°. Find the fourth angle in degrees. Pause the video, and try it.
3:24 The answer is 80.
3:27 Well done! Now try the practice and the quiz in this lesson on LearnFun.
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