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Algebra and geometry · Level 9 of 12

Polynomials, coordinates and geometry

This is where maths becomes a language: equations that describe lines and curves, triangles that measure heights you cannot reach, and patterns that continue for ever. Each topic starts from its key idea and works through the standard method step by step, with graded practice, so you can explain a method as well as use it.

Number systems

Rational and irrational numbers, surds and rational powers.

Key idea

Rational numbers can be written as p/q. Irrational numbers like √2 and π cannot: their decimals never end and never repeat.

How to do it

  1. Terminating or repeating decimal: rational.
  2. Never-ending, never-repeating decimal: irrational.
  3. √(a × b) = √a × √b, so √72 = √36 × √2 = 6√2.
  4. a^(p/q) means: take the qth root, then raise it to the power p.
Practise number systems

Polynomials

Degree, values, zeroes and the remainder and factor theorems.

Key idea

A polynomial is a sum of terms with whole-number powers of x. Putting x = a into it gives p(a). If p(a) = 0, then (x − a) is a factor.

How to do it

  1. The degree is the highest power of x.
  2. To find p(a), put a in place of every x.
  3. Remainder theorem: p(x) ÷ (x − a) leaves remainder p(a).
  4. Factor theorem: if p(a) = 0, then (x − a) is a factor.
Practise polynomials

Coordinate geometry

The four quadrants, points with negative coordinates, and the axes.

Key idea

Every point is (x, y): x is how far right (+) or left (−), and y is how far up (+) or down (−).

How to do it

  1. Quadrant I (+, +), II (−, +), III (−, −), IV (+, −).
  2. A point with y = 0 is on the x-axis. A point with x = 0 is on the y-axis.
  3. The distance from the x-axis is |y|, and from the y-axis is |x|.
Practise coordinate geometry

Linear equations in two variables

Solutions of ax + by = c, and seeing them as a straight line.

Key idea

An equation like 2x + y = 6 has infinitely many solutions. Plotted on a graph, they all lie on one straight line.

How to do it

  1. A solution is a pair (x, y) that makes the equation true.
  2. Put x and y in to check: does the left side equal the right side?
  3. Choose any x, then solve for y to find a solution.
  4. All the solutions together form a straight line.
Practise linear equations in two variables

Lines, triangles & quadrilaterals

Parallel lines, triangle angles, congruence and parallelograms.

Key idea

Parallel lines create equal angles. Triangles add up to 180°. Congruent triangles match exactly, side for side and angle for angle.

How to do it

  1. Corresponding and alternate angles are equal. Co-interior angles add up to 180°.
  2. Angles in a ratio a : b : c: divide 180° into a + b + c parts.
  3. Congruence rules: SSS, SAS, ASA, RHS.
  4. The segment joining the midpoints of two sides is half the third side.
Practise lines, triangles & quadrilaterals

Circles

Chords, the angle at the centre, semicircles and cyclic quadrilaterals.

Key idea

Circle theorems link angles and chords. Most of them come from one fact: the angle at the centre is twice the angle at the edge.

How to do it

  1. Angle at centre = 2 × angle at circumference (same arc).
  2. The angle in a semicircle is 90°.
  3. Opposite angles of a cyclic quadrilateral add up to 180°.
  4. The perpendicular from the centre bisects a chord. Use Pythagoras with the radius.
Practise circles

Heron's formula

The area of any triangle from its three sides.

Key idea

If you know all three sides of a triangle, Heron’s formula gives the area without needing the height.

How to do it

  1. Find s = (a + b + c) ÷ 2.
  2. Work out s − a, s − b and s − c.
  3. Multiply s(s − a)(s − b)(s − c).
  4. Take the square root.
Practise heron's formula

Surface areas & volumes

Cones, spheres, hemispheres and cylinders.

Key idea

Surface area is the outside skin, in square units. Volume is the space inside, in cubic units.

How to do it

  1. Cylinder: volume πr²h, curved surface 2πrh.
  2. Cone: volume ⅓πr²h, curved surface πrl (l is the slant height, l² = r² + h²).
  3. Sphere: volume ⁴⁄₃πr³, surface 4πr².
  4. Hemisphere: curved surface 2πr², total surface 3πr².
Practise surface areas & volumes

Statistics

Frequency tables, class marks, mean and median.

Key idea

A frequency table counts how often each value appears. The mean is Σfx ÷ Σf.

How to do it

  1. Multiply each value by its frequency (fx).
  2. Add them up (Σfx) and add the frequencies (Σf).
  3. Mean = Σfx ÷ Σf.
  4. Class mark = (lower limit + upper limit) ÷ 2.
Practise statistics