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Question

In $\Delta\text{XYZ}$, $\text{XY} = 12\text{ cm}$ and $\text{YZ} = 18\text{ cm}$. $\text{XW}$, the angle bisector of $\text{YXZ}$, meets $\text{YZ}$ at $\text{W}$, such that $\text{YW} : \text{WZ}$ is $4 : 5$. Find the length of the third side of the triangle.

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
$15\text{ cm}$

Triangle Geometry: Angle Bisector Theorem

The problem involves finding the length of the third side of a triangle using the Angle Bisector Theorem.

Given:

  • Triangle $\Delta\text{XYZ}$
  • Side lengths: $\text{XY} = 12\text{ cm}$, $\text{YZ} = 18\text{ cm}$
  • XW is the angle bisector of $\angle\text{YXZ}$, meeting $\text{YZ}$ at W.
  • Ratio: $\text{YW} : \text{WZ} = 4 : 5$
  • To find: Length of side $\text{XZ}$.

Applying the Angle Bisector Theorem

The Angle Bisector Theorem states that an angle bisector of a triangle divides the opposite side into two segments that are proportional to the other two sides of the triangle.

For $\Delta\text{XYZ}$ and angle bisector XW:

$ \frac{\text{YW}}{\text{WZ}} = \frac{\text{XY}}{\text{XZ}} $

Calculation

We are given the ratio $\frac{\text{YW}}{\text{WZ}} = \frac{4}{5}$ and the side length $\text{XY} = 12\text{ cm}$.

Substitute these values into the Angle Bisector Theorem equation:

$ \frac{4}{5} = \frac{12\text{ cm}}{\text{XZ}} $

To find $\text{XZ}$, rearrange the equation:

$ \text{XZ} = \frac{12\text{ cm} \times 5}{4} $

Calculate the result:

$ \text{XZ} = \frac{60\text{ cm}}{4} $ $ \text{XZ} = 15\text{ cm} $

Result

The length of the third side, $\text{XZ}$, is $15\text{ cm}$.

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Similar Questions

  1. In $\triangle ABC$, $BD \perp AC$ at $D$ and $\angle DBC = 40^\circ$. $E$ is a point on $BC$ such that $\angle CAE = 37^\circ$. What is the measure of $\angle AEB$?
  2. In $\Delta ABC$, $BD \perp AC$ at D and $\angle DBC = 71^\circ$. E is a point on BC such that $\angle CAE = 17^\circ$. What is the measure of $\angle AEB$?
  3. In triangle ABC, bisector of $\angle\text{ABC}$ and $\angle\text{ACB}$ meet at O. If $\angle\text{BAC} = 60^\circ$, then find the measure of $\angle\text{BOC}$.
  4. In $\Delta\text{PQR}$, $\text{QR}$ is extended up to $\text{S}$ so that $\text{RS} = \text{RP}$. If $\angle\text{PRQ} = 70^\circ$ and $\angle\text{QPS} = 110^\circ$ then find the measure of $\angle\text{PQS}$.
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Important Questions from Triangles

  1. What is the foot of the altitude from the vertex A of the triangle ABC?

  2. In ΔABC, D is a point on BC such that ∠ADB = 2∠DAC, ∠BAC = 70° and ∠B = 56°. What is the measure of ∠ADC?

  3. In ΔABC, ∠A = 66° and ∠B = 50 °. If the bisectors of ∠B and ∠C meet at P, then ∠BPC – ∠PCA = ?

  4. In a triangle ABC, points P and Q are on AB and AC, respectively, such that AP = 4 cm, PB = 6 cm, AQ = 5 cm and QC = 7.5 cm. If PQ = 6 cm, then find BC (in cm).

  5. The perimeters of two similar ΔABC and  Δ PQR are 48.4 cm and 12.1 cm, respectively. What is the ratio of the areas of  Δ ABC and  Δ PQR?

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