Practicing Success
In $\triangle ABC, \angle C = 90^\circ$, AC = 5 cm and BC = 12 cm. The bisector of $\angle A$ meets BC at D. What is the length of AD? |
$\frac{2}{3}\sqrt{13}$ cm $\frac{4}{3}\sqrt{13}$ cm $2\sqrt{13}$ cm $\frac{5\sqrt{13}}{3}$ cm |
$\frac{5\sqrt{13}}{3}$ cm |
BC = 12 , AC = 5 In \(\Delta \)ABC \( {(AB) }^{2 } \) = \( {(AC) }^{2 } \) + \( {(BC) }^{2 } \) = \( {(AB) }^{2 } \) = \( {(5) }^{2 } \) + \( {(12) }^{2 } \) = 25 + 144 = 169 AB = \(\sqrt {169 }\) = 13 As, AD is the bisector of \(\angle\)A. = \(\frac{AC}{AB}\) = \(\frac{CD}{DB}\) = \(\frac{5}{13}\) = \(\frac{CD}{DB}\) Suppose CD : DB = 5x : 13x BC = CD + DB 12 = 5x + 13x 18x = 12 x = \(\frac{12}{18}\) = \(\frac{2}{3}\) CD = 5 x \(\frac{2}{3}\) = \(\frac{10}{3}\) In \(\Delta \)ACD \( {(AD) }^{2 } \) = \( {(CD) }^{2 } \) + \( {(AC) }^{2 } \) \( {(AD) }^{2 } \) = \( {(\frac{10}{3}) }^{2 } \) + \( {(5) }^{2 } \) \( {(AD) }^{2 } \) = \(\frac{100}{9}\) + 25 \( {(AD) }^{2 } \) = \(\frac{100\;+\;225}{9}\) = \(\frac{325}{9}\) AD = \(\frac{5\sqrt {13 }}{3}\). Therefore, AD is \(\frac{5\sqrt {13 }}{3}\) cm. |