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Congruence and similarity

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교육자를 위해: Congruence and similarity(Mathematics, Geometry and measures)을(를) 위한 바로 쓸 수 있는 수업 슬라이드, 복습 노트 — 수업에 사용하거나, 학습자들이 실시간 게임으로 즐기는 인터랙티브 클래스 활동으로 진행하세요.

수업 노트

Congruent shapes

  • Shapes are congruent if they are exactly the same shape and size (one can be rotated, reflected or translated onto the other).
  • Triangles are congruent if one of these holds: SSS (three sides equal), SAS (two sides and the included angle), ASA or AAS (two angles and a side), RHS (right angle, hypotenuse and a side).
  • AAA is not enough: it gives similar triangles, not congruent ones.

Congruent triangles can be turned

Congruent triangles can be turned4 cm3 cm5 cm4 cm3 cm5 cmSame corresponding lengths; orientation may change.

Similar shapes

  • Shapes are similar if corresponding angles are equal and corresponding sides are in the same ratio — the scale factor.
  • Scale factor = new length ÷ original length. A rectangle 3 × 5 enlarged to 6 × 10 has scale factor 2.

Similar triangles: length factor 2

Similar triangles: length factor 24 cm3 cm5 cm8 cm6 cm10 cmCorresponding lengths are multiplied by 2.

Areas and volumes of similar shapes

  • If the length scale factor is k, then area scales by k2 and volume scales by k3.
  • Scale factor 3: lengths × 3, areas × 9, volumes × 27.
  • Ratio of areas = (ratio of lengths)²; ratio of volumes = (ratio of lengths)³.

Lengths, areas and volumes

Lengths, areas and volumesLength factorArea factorVolume factor2483927

Using similar triangles

  • Set up equal ratios of corresponding sides: if triangle ABC ~ DEF with AB = 4, DE = 6, BC = 5, then EF = 5 \times \frac{6}{4} = 7.5.
  • Parallel lines cut by transversals create similar triangles, with equal corresponding angles.

슬라이드

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연습 문제

무료 미리 보기 — 31개 중 8개 문제. 가입하면 전부 볼 수 있어요.
  1. 1.What does 'congruent' mean for two shapes?

    Easy
    • Asame shape and size
    • Bsame shape, different size
    • Csame area only
    • Dsame perimeter only
  2. 2.Which pair of shapes is always similar?

    Easy
    • Aany two rectangles
    • Bany two circles
    • Cany two triangles
    • Dany two rhombuses
  3. 3.What is the scale factor of an enlargement from a 4 cm side to a 12 cm side?

    Easy
    • A3
    • B8
    • C4
    • D16
  4. 4.Triangle ABC has sides 3, 4, 5 and DEF has sides 6, 8, 10. Are they similar?

    Easy
    • Ayes, scale factor 2
    • Bno
    • Cyes, scale factor 3
    • Dcongruent
  5. 5.Which condition proves two triangles congruent: two sides and the angle between them?

    Easy
    • ASSS
    • BSAS
    • CAAA
    • DRHS
  6. 6.Which condition proves two right-angled triangles congruent using the hypotenuse and one side?

    Easy
    • ASSS
    • BSAS
    • CRHS
    • DAAA
  7. 7.A rectangle 3 cm by 5 cm is enlarged by scale factor 2. What are its new dimensions?

    Easy
    • A5 by 7
    • B6 by 10
    • C9 by 15
    • D6 by 5
  8. 8.The scale factor is 3. By what factor is the area multiplied?

    Easy
    • A3
    • B6
    • C9
    • D27

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