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In an equilateral triangle ABC of side 10cm, the side BC is trisected at D. Then the length (in cm) of AD is
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- 3√7
- 7√3
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10√7 3 -
7√10 3
- 3√7
Correct Option: C
AE ⊥ BC
∴ BE = EC = 5 cm
AC = 10 cm
AE = √10² - 5²
= √100 - 25 = √75
= 5√3 cm
DE = DC – EC
| = | × 10 - 5 = | cm. | ||
| 3 | 3 |
| ∴ AD = √ |  |  | ² | + (5√3)² | |
| 3 |
| = √ | + 75 | |
| 9 |
| = √ | ||
| 9 |
| = √ | = | cm | ||
| 9 | 3 |
