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Question

What is the angle at $B$ in the triangle $ABC$, if the angle made at $K$ is $30^\circ$ and the triangles shown in the figure are similar?

This question was previously asked in
RRB ALP/Technician 2018 CBT 2 Electronics Mechanic Question Paper (23-Jan-2019) (Shift 1)
The correct answer is

$30^\circ$

To find the angle at \(B\) in triangle \(ABC\), given that the triangles are similar and the angle at \(K\) is \(30^\circ\), we need to analyze the properties of similar triangles.

Step 1: Understand Similarity in Triangles

Two triangles are similar if their corresponding angles are equal and their corresponding sides are proportional. In this case, the similarity of the triangles implies all corresponding angles between the triangles are equal.

Step 2: Identify Corresponding Angles

From the diagram, if \(\triangle KJL\) is similar to \(\triangle ACB\), then:

  • \(\angle K = \angle A\)
  • \(\angle J = \angle C\)
  • \(\angle L = \angle B\)

Since we know \(\angle K = 30^\circ\), this implies that \(\angle A = 30^\circ\).

Step 3: Calculate and Confirm Angle at B

Given that the triangles are similar, the corresponding angles are equal:

Therefore, \(\angle B = \angle L = 30^\circ\).

Conclusion:

The angle at \(B\) in triangle \(ABC\) is \(30^\circ\).

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Similar Questions

  1. In the given figure, if \(RS = 3\sqrt{3} \text{ cm}\) and \(RPS\) is an equilateral triangle, then find the value of \(QR\)

  2. In a right angled triangle, with angle at \(A\) being \(90^\circ\), the side \(AB\) is of length 3cm and \(BC\) is 12 cm. What is the length of side \(AC\)?
  3. For a pair of similar triangles shown in the figure, the angles made at $B$ and $R$ are same in both the triangles $BAC$ and $RAQ$. If the ratio of the areas of the two triangles is 2:1, and if the area of $BAC$ is $100\text{ cm}^2$ then what is the area of $RAQ$ in sq.cm.?

  4. In a triangle $ABC$, the length of the side $AB$ is 2m, the angle at $C$ is $60^\circ$ and the angle at $B$ is $30^\circ$, what is the length of side $AC$?
  5. In a right angled triangle, with angle at A being , the side $AB$ is of length 4cm and $BC$ is 15 cm. What is the length of side $AC$?

     

     

  6. Triangles $PQR$ and $ABC$ are similar triangles.
    Triangle $ABC$ have the following sides.
    $AB = 36\text{ cm}$
    $AC = 20\text{ cm}$
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  7. What is the area of the triangle in sq. cm. with a base of 10 cm and sides of length 6 cm each?
  8. In a triangle the length of the sides, $AB$ is 3m and $BC$ is 5m what is the length of $AC$, if the angle formed at $B$ is $60^\circ$
  9. In a triangle \(\Delta ABC\ AB= 13\text{ cm}, BC=84\text{cm}, \text{and } \angle B=90^\circ\), then length of AC will be
  10. Which of the following is not a Pythagorean triplet?

Important Questions from Triangles

  1. What is \(AB + BC\) equal to?
     

  2. In the given figure, if \(RS = 3\sqrt{3} \text{ cm}\) and \(RPS\) is an equilateral triangle, then find the value of \(QR\)

  3. In a right angled triangle, with angle at \(A\) being \(90^\circ\), the side \(AB\) is of length 3cm and \(BC\) is 12 cm. What is the length of side \(AC\)?
  4. For a pair of similar triangles shown in the figure, the angles made at $B$ and $R$ are same in both the triangles $BAC$ and $RAQ$. If the ratio of the areas of the two triangles is 2:1, and if the area of $BAC$ is $100\text{ cm}^2$ then what is the area of $RAQ$ in sq.cm.?

  5. In a triangle $ABC$, the length of the side $AB$ is 2m, the angle at $C$ is $60^\circ$ and the angle at $B$ is $30^\circ$, what is the length of side $AC$?
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