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    Question

    In an acute-angled triangle XYZ, an altitude XP is drawn

    from vertex X to side YZ. A point O is located on XP such that XY = 12 cm, OY = 5 cm, and OZ = 9 cm. Determine the length of XZ.
    A 10√2 cm Correct Answer Incorrect Answer
    B 20 cm Correct Answer Incorrect Answer
    C 12√5 cm Correct Answer Incorrect Answer
    D 20 cm Correct Answer Incorrect Answer

    Solution

    Image Since, XP ⊥ YZ, both ΔXYP and ΔOYP are right triangles.Similarly, both ΔXZP and ΔOZP are also right triangles.Using Pythagoras theorem, we have;In ΔXYP, XY2 = YP2 + XP2Or, XP2 = XY2 - YP2 ....... (I)And ΔXZP, we have;XZ2 = XP2 + PZ2So, XP2 = XZ2 - PZ2 ...... (II)So, XY2 - YP2 = XZ2 - PZ2Now, using equation (I) and (II) , we have;Or, XZ2 - XY2 = PZ2 - YP2 ...... (III)Now, in ΔOYP, we have;And OP2 = OY2 - YP2 ....... (IV)And in ΔOZP, we have;OP2 = OZ2 - PZ2 ...... (V)Now, using equation (IV) and (V) , we have;OY2 - YP2 = OZ2 - PZ2Or, PZ2 - PY2 = OZ2 - OY2 ...... (VI)Now, using equation (III) and (VI) , we have;OZ2 - OY2 = XZ2 - XY2Or, XY2 + OZ2 = XZ2 + OY2So, 122 + 92 = XZ2 + 52Or, 144 + 81 = XZ2 + 25Or, XZ2 = 225 - 25Or, XZ2 = 200And XZ = ± 10√2Since, side of a triangle cannot be negative, XZ = 10√2 cm

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