Mathematics (គណិតវិទ្យា)
What the paper tests
Grade 9 mathematics tests algebra, linear and quadratic equations, ratio and proportion, geometry including Pythagoras’ theorem, area and volume, and basic statistics. Marks are lost less from hard ideas than from untidy algebra and missing units.
Core rules and concepts
- Solve linear equations by doing the same operation to both sides.
- A quadratic in the form ax² + bx + c = 0 can often be solved by factorising.
- Pythagoras: in a right triangle, a² + b² = c², where c is the hypotenuse.
- Area and volume formulas must use consistent units; convert centimetres to metres before calculating.
- Mean = sum of values ÷ number of values.
Worked example
Solve x² − 5x + 6 = 0. Find two numbers that multiply to +6 and add to −5: they are −2 and −3. So x² − 5x + 6 = (x − 2)(x − 3) = 0. Therefore x = 2 or x = 3. Check: 2² − 5(2) + 6 = 4 − 10 + 6 = 0; 3² − 5(3) + 6 = 9 − 15 + 6 = 0. Both roots satisfy the equation.
Traps that cost marks
Do not divide both sides by a variable such as x; you may lose the root x = 0. Watch signs when factorising. In geometry, do not use Pythagoras unless the triangle is right-angled. Always write the unit in the final answer.
Exam focus
Show the factorisation line, not only the final roots; method marks are awarded for correct steps.