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Triangles

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A photo can be printed bigger. Its shape does not change.

Every side of the small triangle × 2 gives the large one.

This is Chapter 6, Triangles, in your Class 10 book. It gives "same shape" a precise meaning. Then it proves one theorem about a line parallel to a side.

What you will learn

  • Similar figures. Equal angles and one ratio of sides.
  • AA. Angle, angle: two matching angles are enough.
  • SSS. Side, side, side: three side ratios match.
  • SAS. Side, angle, side: two side ratios and the angle between them.
  • Shadows. A pole and its shadow measure a tall tree.
  • The parallel-line theorem. A parallel line splits two sides in one ratio.
  • The converse. Equal splits mean the line is parallel.
  • The corner triangle. The parallel makes a smaller similar triangle.
  • Which test. Match the corners, then choose the test.

Jump to lesson

This track

  1. 0 Start here
  2. 1 Similar, said precisely
  3. 2 Two angles are enough
  4. 3 Sides in the same ratio
  5. 4 Two sides and the angle between
  6. 5 Heights without ladders
  7. 6 Checkpoint: shapes, factors and shadows
  8. 7 A line parallel to one side
  9. 8 Reading the split backwards
  10. 9 Checkpoint: the parallel-line pair
  11. 10 From a parallel to a similarity
  12. 11 Which test decides it
  13. 12 The big picture
  14. 13 Track quiz

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