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No. 111 History of Mathematica in India from faina Sources 61
2. PARALLELOGRAM : The area of a parallelogram is equal to the length of its base multiplied by its height.
Fig. 6
Construction. Cut the portion (4 perpendicular to #9) and take it to the other side (06). The resultir:g figure is a rectangle, hence the theorem.
First Principle of Deformation: If one of the sides of a parallelo gram is moved along itself, the area of the parallelogram remains unchanged.
In the figure 9 a 7; 8 sliding in its own line is moved to the position giving the rectangle of equal arca.
3. TRIANGLE: The area of a triangle is equal to half the length of its base multiplied by its height.
This result is true because a triangle is half of a parallelogram on the same base and of the same height.
Second principle of deformation. If the vertex of a triangle is moved parallel to the base, the area of the triangle remains unchanged.
Fig. 7.
