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Term |
Definition |
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| radian | unit for measuring angles. $$\pi^r$$= 180° and 2$$\pi$$ = 360°. $$1^r=\frac$$ and 1° =$$\frac$$ | ||||||||||||||
| radius | the name given to a line from the centre of a circle to the circumference. The radius is half the length of the diameter. The radius will also meet the tangent in a right angle. | ||||||||||||||
| random | term in probability when each selection is just as likely as another. to choose randomly means that there is no reason one would be picked more than another. | ||||||||||||||
| range | the highest score minus the lowest score | ||||||||||||||
| range of function | refers to the y values a function can take. For example the range of y = x2 is R: [0, ∞) | ||||||||||||||
| rate | the amount one quantity changes with respect to another. Speed is the most commonly used rate, km/h measures how many kilometres are travelled over time. Rates are expressed in the terms of two units, unit1 per unit2, or such as words per minute, litres/minute | ||||||||||||||
| ratio | a comparison between two amounts. Ratios are generally unit free, and whole numbers. An example of 50 m:1 km would be simplified to 50:1000 and then down to 1:20 | ||||||||||||||
| rational number | any number that can be expressed as a whole number, fraction, finite or recurring decimal | ||||||||||||||
| ray | half a line. Starting from a point and extending in only one direction, instead of both
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| real number | all rational and irrational numbers | ||||||||||||||
| reciprocal | the upside down fraction, or when 1 is divided by the number. for example the reciprocal of 7/9 is 9/7 or the reciprocal of 2 is 1/2, the reciprocal of $$\frac$$ is $$\frac$$ | ||||||||||||||
| rectangle | quadrilateral with opposite sides equal and parallel. Diagonals are equal and bisect each other. Adjacent sides perpendicular |
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| rectangular numbers | all numbers that have more than two factors and can be represented by dots forming a rectangle. For example 6 is a rectangular number. The first rectangular number is 2 × 1 = 2, the second would be 3 × 2 = 6, the third would be 4 × 3 = 12 and so on.
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| rectangular prism | solid shape made up of six rectangles, with a rectangular cross section. A box.
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| rectilinear | motion in a straight line | ||||||||||||||
| recurring decimal | decimal with a digit, or series of digits repeated infinitely. 1/3 = 0.333333333333… | ||||||||||||||
| re-entrant | polygon with one angle more than 180°, also known as a concave polygon | ||||||||||||||
| reflection | transformation that 'flips' a shape in the line of reflection | ||||||||||||||
| reflex angle | angle more than 180° but less than 360° | ||||||||||||||
| region | area of a graph that is defined by an inequality | ||||||||||||||
| regular polygon | polygon with all equal sides and equal angles | ||||||||||||||
| relative frequency | the proportion of times data occurs in a distribution. The relative frequency is obtained by dividing how many times that score occurs by the total number of scores | ||||||||||||||
| remainder | how much is left over when something is divided and it does not fit evenly | ||||||||||||||
| remainder theorem | when P(x) is divided by (x – a), then the remainder will be P(a) | ||||||||||||||
| revolution | angle at a point, full turn angle, 360° | ||||||||||||||
| rhombic prism | a prism with a rhombus as a cross section
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| rhombus |
a quadrilateral (4 sides) with opposite sides parallel and all sides equal. Also called a 'diamond' or a 'squishy square'. Diagonals bisect at right angles.
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| right angle | angle formed when two lines meet at 90°, or are perpendicular. Right angles are indicated with a little square.
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| right pyramid | Pyramid with its vertex directly over the centre of the base  |
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| roman numerals |
Number system the Romans used to use.
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| root | The solution to an equation. | ||||||||||||||
| root | Shortened version of square root | ||||||||||||||
| rotate | to turn | ||||||||||||||
| rotation | the act of turning | ||||||||||||||
| rotation | transformation where a shape is moved around a fixed point | ||||||||||||||
| rotational symmetry | when a shape can be rotated so that it fits exactly onto its own outline more than once in a full turn | ||||||||||||||
| rounding off | writing a number correct to a specified number of decimal places. See Rounding page for fully worked examples and explanations. | ||||||||||||||
| rpm | abbreviation for revolutions per minute. How many time something turns around completely in one minute. |
