Ch 6 covers triangle fundamentals: medians, altitudes, the angle sum property (180°), the exterior angle theorem, types of triangles, the triangle inequality property, and the Pythagoras theorem for right-angled triangles.
A median joins a vertex to the midpoint of the opposite side. An altitude is the perpendicular from a vertex to the opposite side. Every triangle has three medians and three altitudes.
The sum of interior angles of a triangle is always 180°. An exterior angle of a triangle equals the sum of the two opposite (remote) interior angles. This is the exterior angle theorem.
In a right-angled triangle, the square of the hypotenuse equals the sum of squares of the other two sides: a² + b² = c². A set of three numbers satisfying this (like 3, 4, 5) is called a Pythagorean triplet.
Download: https://ncert.nic.in/textbook/pdf/gemh106.pdf | Complete book: https://ncert.nic.in/textbook/pdf/gemh1ps.zip
The sum of any two sides of a triangle must be greater than the third side. If this condition is not met, the three lengths cannot form a triangle.
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