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A parallelogram has sides 15 cm and 7 cm long. The length of one of the diagonals is 20 cm. The area of the parallelogram is
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- 42 cm²
- 60 cm²
- 84 cm²
- 96 cm²
- 42 cm²
Correct Option: C
Using Rule 2 and 3,
Area of parallelogram ABCD
= Area of 2 ∆ ABC
Semi-perimeter of ∆ ABC
| S = | = | = 21 cm | ||
| 2 | 2 |
∴ area of ∆ ABC
= √s(s - a)(s - b)(s - c)
= √21(21 - 7)(21 - 20)(21 - 15)
= √21 × 14 × 6 = 42 sq.cm.
∴ Area of parallelogram = 2 × 42 = 84 sq. cm.
