Multiplying or dividing an inequality by a negative number reverses its direction: −2x > 4 gives x < −2.
A linear equation may be an identity (every number is a solution) or a contradiction (no solutions).
Quadratic equation ax² + bx + c = 0: Δ = b² − 4ac. If Δ > 0: x = (−b ± √Δ)/(2a). If Δ = 0: x = −b/(2a). If Δ < 0: no real solutions.
Solve a quadratic inequality using the zeros and a sketch of the parabola: if a > 0, the negative values lie between the zeros.
An equation in factored form: a product equals 0 when one of its factors equals 0.
Do not divide both sides by an expression with x without checking its sign and zero: solutions can be lost. With fractions, state the assumption: the denominator is not 0.
Solve a system of two linear equations by substitution or by elimination.
A determined system has one solution: the lines intersect. An indeterminate system has infinitely many solutions: the lines coincide. An inconsistent system has no solutions: the lines are parallel and different.
Always check the solution in both equations.
In a word problem, name two unknowns and write two independent conditions.
A function assigns exactly one value to each argument in its domain. The domain is the set of arguments; the range is the set of values of the function.
A zero of a function is an argument for which f(x) = 0. On the graph: the point where it crosses the x-axis.
The graph of y = f(x − a) is the graph of f shifted a to the right (for a > 0). The graph of y = f(x) + b is the graph of f shifted b up (for b > 0).
The function f(x) = a/x describes inversely proportional quantities: the product x · f(x) is constant and equals a.
The exponential function f(x) = aˣ (a > 0, a ≠ 1) is increasing for a > 1 and decreasing for 0 < a < 1; its values are positive.
The logarithmic function f(x) = logₐ x has domain (0, +∞) and the zero x = 1.
In a right-angled triangle: sin α = opposite leg / hypotenuse; cos α = adjacent leg / hypotenuse; tg α = opposite leg / adjacent leg (tg is the Polish notation for tan).
Values: sin 30° = cos 60° = 1/2; sin 45° = cos 45° = √2/2; sin 60° = cos 30° = √3/2; tg 30° = √3/3; tg 45° = 1; tg 60° = √3.
Identities: sin²α + cos²α = 1 and tg α = sin α / cos α.
For an obtuse angle: sin α > 0, cos α < 0, tg α < 0, and sin(180° − α) = sin α, cos(180° − α) = −cos α.
Cosine rule: c² = a² + b² − 2ab · cos γ.
Area of a triangle: A = (1/2) · a · b · sin γ, where γ is the angle between sides a and b.
An inscribed angle is half the central angle on the same arc. An inscribed angle on a diameter is a right angle.
A tangent is perpendicular to the radius at the point of tangency. Tangent segments drawn from one point are equal.
A sector with angle α: area = (α/360°) · πr², arc length = (α/360°) · 2πr.
Thales' theorem: parallel lines cut proportional segments on the arms of an angle.
Similar figures with scale k: perimeters are in the ratio k, and areas in the ratio k².
Type of triangle with longest side c: a² + b² > c² acute, a² + b² = c² right-angled, a² + b² < c² obtuse.
Special points: incentre (angle bisectors), circumcentre (perpendicular bisectors), centroid (medians, ratio 2 : 1), orthocentre (heights). In a right-angled triangle R = c/2 and r = (a + b − c)/2.
Area of a regular hexagon with side a: 6 · a²√3/4.
Prism: V = B · H. Pyramid: V = (1/3) · B · H, where B is the base area.
Cylinder: V = πr²H, L = 2πrH. Cone: V = (1/3)πr²H, L = πrl, where l² = r² + H². Sphere: V = (4/3)πr³, S = 4πr².
Diagonal of a cube with edge a: a√3. Diagonal of a cuboid: √(a² + b² + c²).
The angle between a line and a plane is the angle between the line and its projection on the plane, e.g. the angle of a space diagonal with the base diagonal.
The angle between a lateral face and the base of a regular square pyramid: tg α = H : (a/2).
Similar solids with scale k: surface areas in the ratio k², volumes in the ratio k³.
Skew lines do not meet and are not parallel; they may be perpendicular, e.g. the edges AB and CG of a cube.
27^(2/3) = (∛27)² = 3² = 9, and 3^(−1) = 1/3. The product: 9 · 1/3 = 3.
Question 2 · Logarithms
Calculate log₃ 81.
Answer: 4
3⁴ = 81, so log₃ 81 = 4.
Question 3 · Percentages, deposits and loans
5000 zł was placed on a one-year deposit at an interest rate of 4% per year. How many złoty will be on the deposit after a year? Ignore tax.
Answer: 5200
Interest: 4% · 5000 = 200 zł. Total: 5000 + 200 = 5200 zł.
Question 4 · Algebraic expressions
The expression (x − 3)² equals:
x² − 6x + 9
x² − 9
x² + 9
x² − 3x + 9
Answer: x² − 6x + 9
(a − b)² = a² − 2ab + b², so x² − 2 · x · 3 + 9 = x² − 6x + 9. The form x² − 9 leaves out the middle term.
Question 5 · Equations and inequalities
The solution set of the inequality 3x − 5 ≤ 7 is the interval:
(−∞, 4]
(−∞, 4)
[4, +∞)
(−∞, 2/3]
Answer: (−∞, 4]
3x ≤ 12, so x ≤ 4. The inequality is not strict, so 4 belongs to the set, hence the square bracket.
Official CKE papers
The page for each year has the papers and marking rules for every subject. We only link to them; CKE publishes the materials. These are Formula 2023 papers.
CKE trial papers appear on the CKE website on the day of publication.
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