1. Warm-Up Find the length of the altitude in an equilateral triangle with a side length of 10 cm. Find the area of each triangle:

2. Section 10-1 Area of Parallelograms &Triangles Objectives: find area of a parallelogram and triangle Area = base x height A = bh h b Area = ½ base x height A = ½ bh h b

3. Why is it just like l x w? So a parallelogram with the given b and h is the same as a rectangle with b = l and h = w.

4. Finding Area of a Parallelogram Base of a parallelogram is any of its sides The corresponding altitude is a segment  to the line containing the base, drawn from the opposite side of the base. The height is the length of the altitude.

5. Find the area of a Parallelogram What is the area of the parallelogram? Find the area of PQRS with vertices P(1, 2), Q(6, 2), R(8, 5) and S(3, 5). 1. Graph the parallelogram. 2. Choose the base. 3. Substitute in A = bh. A = bh = 2(3.5) = 7 cm 2 b = PQ = 5 h = 3 A = bh = 5(3) = 15

6. A parallelogram has 9-in. and 18-in. sides. The height corresponding to the 9-in. base is 15 in. Find the height corresponding to the 18-in. base. Find the area of the parallelogram using the 9-in. base and its corresponding 15-in. height. A = bhArea of a parallelogram A = 9(15)Substitute 9 for b and 15 for h. A = 135Simplify. The area of the parallelogram is 135 in. 2 Find a missing dimension Use the area 135 in. 2 to find the height to the 18-in. base.

7. The height corresponding to the 18-in. base is 7.5 in. A = bhArea of a parallelogram 135 = 18hSubstitute 135 for A and 18 for b. = hDivide each side by 18. 7.5 = hSimplify. 135 18..... continued