Ch 6 covers similarity of triangles, the Basic Proportionality Theorem (BPT/Thales theorem), criteria for similarity (AA, SSS, SAS), relationship between areas, and the proof of Pythagoras theorem.
If a line is drawn parallel to one side of a triangle, it divides the other two sides proportionally. Converse: if a line divides two sides proportionally, it is parallel to the third side.
AA (Angle-Angle): if two angles of one triangle equal two angles of another. SSS: if all three pairs of sides are proportional. SAS: if two pairs of sides are proportional and the included angles are equal.
The ratio of areas of similar triangles = square of the ratio of corresponding sides. Pythagoras theorem (proved using similarity): in a right triangle, the square of the hypotenuse equals the sum of squares of the other two sides.
Download: https://ncert.nic.in/textbook/pdf/jemh106.pdf | Complete book: https://ncert.nic.in/textbook/pdf/jemh1ps.zip
Congruent triangles are identical in both shape and size. Similar triangles have the same shape but can differ in size — their corresponding angles are equal and sides are proportional.
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