JM28 · Lesson 28
Special Line and Centres in Triangles
Special lines & centres, angle pairs on parallel lines, then congruence and similarity — with standard geometry markings.
Click / Space = next. Left = previous. The key property of each centre, and which centres can lie outside the triangle.
Lab 1 · Special lines & centres
Four special lines → four centres
Construction lines are dashed. Side extensions beyond a vertex use dotted lines. Equal lengths use red ticks; equal angles and right angles use blue marks. Drag vertices to explore.
Shape presets (click to load):
Detected from the current shape:
Lab 2 · Angle pairs (parallel lines)
Corresponding · alternate · interior on same side
Two parallel lines cut by a transversal. Drag the blue handles left/right only to tilt the transversal; pick a relationship to highlight matching angles.
Lab 3 · Congruence & similarity
Congruent △ · Similar △
Switch between congruence and similarity. Drag vertices of △ABC; △DEF follows. Markings show what must match for each condition.
Drag A, B or C — the second triangle updates with you.
JM28 · Meeting Point
三線交會
畫出三條正確的特殊線，讓它們交會成指定中心，點亮水晶。不是選擇題——動手拖線才算數。
從頂點拖到對邊中點。三條中線交於重心。
三線交會
你是線匠。從藍色把手拖出特殊線，對準中點／垂足／平分方向後鬆手。三線交會就點亮水晶。
通關
挑戰失敗
再試一次！
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Summary
Coming soon.
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