
【Deductive Geometry 演繹幾何 Reasoning】直線│平行線│三角形│四邊形│多邊形│圓形【完整列表】
Deductive Geometry(演繹幾何)是中學數學中最麻煩的課題之一, 涵蓋角度、平行線、三角形、四邊形、多邊形及圓形的基本性質與證明技巧。 無論是 HKDSE,還是一般校內測驗,幾何證明題都經常出現, 而掌握核心定理與 abbreviations(簡寫)更是不掉分的關鍵。 Deductive Geometry 演繹幾何 概覽 Angles related to lines & points 直線&點與角 Parallel Lines 平行線 Triangle 三角形 Congruent Triangle 全等三角形 Similar Triangle 相似三角形 Four Centre of Triangle 三角形四心 Parallelogram 平行四邊形 Other Quadrilaterals 其他四邊形 Convex Polygon 凸多邊形 Basic Properties of Circles 圓的基本性質 Angles related to lines & points 直線&點與角 同頂角 (Angles at a point) Given a, b and c are angles at a point Result a + b + c = 360° Abbr. ∠s at a pt. 直線上的鄰角 (Adjacent angles on a straight line) Given a and b are adjacent angles on a straight line Result a + b = 180° Abbr. adj. ∠s on st. line 對頂角 (Vertical opposite angles) Given Two straight lines AB and CD intersect at point O Result a = b and c = d Abbr. vert. opp. ∠s Parallel Lines 平行線 同位角 (Corresponding angles) Given AB // CD Result a = b Abbr. corr. ∠s Given a = b Result AB // CD Abbr. corr. ∠s equal 內錯角 (Alternate angles) Given AB // CD Result c = d Abbr. alt. ∠s Given c = d Result AB // CD Abbr. alt. ∠s equal 同旁內角 (Interior angles) Given AB // CD Result e + f = 180° Abbr. int. ∠s Given e + f = 180° Result AB // CD Abbr. int. ∠s supp. 中點定理 (Mid-point Theorem) Given AM = MB and AN = NC Result MN = 1/2 BC and MN ∥ BC Abbr. mid-pt. thm. 截線定理 (Intercept Theorem) Given L₁ ∥ L₂ ∥ L₃ and AB = BC Result DE = EF Abbr. intercept thm. Triangle 三角形 三角形內角和 (Angle sum of triangle) Given ABC is a triangle Result a + b + c = 180° Abbr. ∠ sum of △ 三角形外角 (Exterior angle of triangle) Given ABC is a △ Result c = a + b Abbr. ext. ∠ of △ 三角不等式 (Triangle Inequality) Given ABC is a △ Result AB + BC > AC, BC + AC > AB, AB + AC > BC Abbr. N/A 等腰三角形 (Isosceles triangle) Given AB = AC Result ∠B = ∠C Abbr. base ∠s, isos. △ Given AB = AC and BD = DC Result ∠BAD = ∠CAD and AD ⟂ BC Abbr. prop. of isos. △ Given AB = AC and AD ⟂ BC Result BD = DC and ∠BAD = ∠CAD Abbr. prop. of isos. △ Given AB = AC and ∠BAD = ∠CAD Result AD ⟂ BC and BD = DC Abbr. prop. of isos. △ Given ∠B = ∠C Result AB = AC Abbr. sides opp. equal ∠s 等邊三角形 (Equilateral triangle) Given AB = BC = AC Result ∠A = ∠B = ∠C = 60° Abbr. prop. of equil. △ Given ∠A = ∠B = ∠C Result BC = AC = AB Abbr. prop. of equil. △ Congruent Triangle 全等三角形 SSS Given AB = XY and AC = XZ and BC = YZ Result △ABC ≅ △XYZ Abbr. SSS SAS Given AB = XY and AC = XZ and ∠A = ∠X Result △ABC ≅ △XYZ Abbr. SAS ASA Given AB = XY and ∠A = ∠X and ∠B = ∠Y Result △ABC ≅ △XYZ Abbr. ASA AAS Given AB = XY and ∠A = ∠X and ∠C = ∠Z Result △ABC ≅ △XYZ Abbr. AAS RHS Given AB = XY and AC = XZ and ∠C = ∠Z = 90° Result △ABC ≅ △XYZ Abbr. RHS Corresponding Sides & Angles Given AB = XY and AC = XZ and △ABC ≅ △XYZ Result BC = YZ Abbr. corr. sides, ≅ △s Given AB = XY and AC = XZ and △ABC ≅ △XYZ Result BC = YZ Abbr. corr. sides, ≅ △s Similar Triangle 相似三角形 AAA Given ∠A = ∠X and ∠B = ∠Y and ∠C = ∠Z Result △ABC ~ △XYZ Abbr. AAA 3 sides proportional Given AB / XY = BC / YZ = CA / ZX Result △ABC ~ △XYZ Abbr. 3 sides prop. 2 sides proportional and included angle equal Given AB / XY = AC / XZ and ∠A = ∠X Result △ABC ~ △XYZ Abbr. ratio of 2 sides, inc. ∠ Corresponding Sides & Angles Given △ABC ~ △XYZ Result AB / XY = BC / YZ = CA / ZX Abbr. corr. sides, ~△s Given △ABC ~ △XYZ Result ∠A = ∠X and ∠B = ∠Y and ∠C = ∠Z Abbr. corr. ∠s, ~△s Four Centre of Triangle 三角形四心 三角形內心 (Incentre) Given I is the incentre of △ABC Result I is the intersection of the angle bisectors, i.e. ∠BAX = ∠CAX, ∠ABY = ∠CBY, ∠BCZ = ∠ACZ Abbr. incentre of △ 三角形外心 (Circumcentre) Given I is the circumcentre of △ABC Result I is the intersection of the perpendicular bisectors, i.e. IX ⟂ BC and BX = XC, IY ⟂ AC and AY = YC, IZ ⟂ AB and AZ = ZB Abbr. circumcentre of △ 三角形形心 (Centroid) Given I is the centroid of △ABC Result I is the intersection of the medians, i.e. AZ = ZB, BX = XC, AY = YC and AI / IX = BI / IY = CI / IZ = 2 / 1 Abbr. centroid of △ 三角形垂心 (Orthocentre) Given I is the orthocentre of △ABC Result I is the intersection of the altitudes, i.e. AX ⟂ BC, BY ⟂ AC, CZ ⟂ AB Abbr. orthocentre of △ Parallelogram 平行四邊形 平行四邊形 (Properties of Parallelogram) Given ABCD is a parallelogram Result AB = DC and AD = BC Abbr. opp. sides of //gram Given ABCD is a parallelogram Result ∠A = ∠C and ∠B = ∠D Abbr. opp. ∠s of //gram Given ABCD is a parallelogram and O is the intersection of diagonals Result AO = OC and BO = OD Abbr. diags. of //gram 證明平行四邊形 (Proof of Parallelogram) Given AB = DC and AD = BC Result ABCD is a parallelogram Abbr. opp. sides equal Given ∠A = ∠C and ∠B = ∠D Result ABCD is a parallelogram Abbr. opp. ∠s equal Given AO








