So the reflex angle is measured indirectly. We cannot directly measure a reflex angle using a protractor, as the maximum it can measure is 180°. Measuring a Reflex AngleĪ reflex angle measures between 180° and 360°. When the second line of the angle points anywhere between 90° to 180° on the protractor, it is an obtuse angle. When the second arm of the angle points to 90° on the protractor, it is a called a right angle. The measurement is recorded from the position of the second arm of the angle on the protractor. Place the protractor such that its center coincides with the vertex of the angle.Įnsure that the 0° line or base line of the protractor coincides with the base arm of the acute angle.
The markings start from 0° and end on 180°. Just like a ruler, a protractor too has markings but in the shape of a half circle. Measuring AnglesĪngles are measured with the help of an instrument known as protractor which is found in a compass box. Complete AngleĪ complete angle is formed when one complete turn or rotation is made by an arm of the angle with respect to the base arm. Reflex AngleĪn angle that lies between 180° and 360° is called a reflex angle. Straight AngleĪ straight angle is formed when the rays forming the angle point in exactly opposite directions.
Obtuse AngleĪngles greater than right angles (90 degrees) but smaller than a straight angle are called obtuse angles. Acute AngleĪngles smaller than right angles (90 degrees) are called acute angles. Right AngleĪn 'L' shaped angle is called a right angle and the arms of the angle make right angle or 90° with each other. The line segments are called the arms of the angle. When two line segments meet at a point, they form an angle. The angles formed by perpendicular lines are called right angles. Two lines making a "+" sign are called perpendicular lines. Two intersecting lines make four angles usually two acute and two obtuse angles. When two lines meet at a point, they are called intersecting lines the meeting point is called the point of intersection. Take the reading from the other arm of the divider. Then, lift the divider and put on the ruler so that one of the arms of the divider coincides with the zero of the ruler. Measuring using a Ruler and a Dividerįirst, take the divider and with its arms stretched, fix it across the endpoints of the line segment. The reading of the other endpoint on the ruler gives the length of the line segment.
Measure the line segment by keeping the ruler along the line segment with the zero of the ruler placed at one endpoint of the line segment. The difference between two big markings on a ruler is 1 cm, while the difference between two small markings on the ruler is 1 mm. The ruler is marked in centimetres and millimetres. When two line segments are nearly of the same length, we have to use a divider to compare their lengths. If we place two line segments side by side, then their lengths can be easily compared just by observing them. The length of a line segment is measured in millimetres and centimetres. Similarly, a quadrilateral can be a rectangle, a square, or a parallelogram. Any complex geometrical shape can be made from these elementary shapes.įor example, a square pyramid is made up of four isosceles triangles and a square base.Ī hexagonal prism is made of 6 rectangles and two hexagons.Įven elementary shapes come in different forms, like a triangle can be an equilateral triangle, an isosceles triangle, or a scalene triangle. Trapezoids must have 4 sides, so they must always be quadrilaterals.Line, angle, triangle, quadrilateral, polygon, and circle are examples of elementary shapes. Here is an example when a parallelogram is not a rectangle: Here is an example when a parallelogram is a rectangle: It is not true when a parallelogram has no right angles. It is true when the parallelogram has 4 right angles. Since rhombuses are quadrilaterals with 4 congruent sides, squares are by definition also rhombuses. Squares are quadrilaterals with 4 congruent sides. Since squares must be quadrilaterals with two sets of parallel sides, then all squares are parallelograms. Parallelograms are quadrilaterals with two sets of parallel sides. Squares are quadrilaterals with 4 congruent sides and 4 right angles, and they also have two sets of parallel sides. A parallelogram is a four-sided figure with two sets of parallel sides. Here is an example when a rhombus is not a square: Here is an example when a rhombus is a square: It is not true when a rhombus does not have any right angles.
It is true when a rhombus has 4 right angles.
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