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4.5 Triangle

Just as the area of parallelogram was derived from the area of rectangle, the area of a triangle can be derived from the area of a parallelogram. Consider the triangle PQR (figure 4.4). If a line is drawn through P parallel to RQ and another line is drawn through Q parallel to PR they will intersect at O. POQR is a parallelogram with PQ as its diagonal.

Figure 4.4

Recall that the diagonal of a parallelogram divides the parallelogram into two congruent triangles.

\ Area of parallelogram POQR = 2 ´ Area D PQR or

Area D PQR = Area of parallelogram POQR.

Area of parallelogram POQR = bh where h is the altitude on the base with length h.

\ Area D PQR = bh

Area of a triangle is half the product of one base and the corresponding altitude.

The perimeter of the triangle is simply the sum of all its sides.

P = ( a + b + c ) in figure 4.4.

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4.1 Perimeter
4.2 Square
4.3 Rectangle
4.4 Parallelogram
4.5 Triangle
4.6 Trapezoids
4.7 Circles

Chapter 5

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