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Question

In $\Delta ABC$, if $\angle A = 3\angle B$ and $\angle C = 2\angle B$ then, what are values of $\angle A, \angle B$ and $\angle C$?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper (8-Mar-2021) (Shift 2)
The correct answer is
$90^\circ$ , $30^\circ$ and $60^\circ$

Solving Triangle Angles A B C

The problem requires finding the measures of the three angles in a triangle, $\angle A$, $\angle B$, and $\angle C$, given specific relationships between them. We know that the sum of the interior angles in any triangle is always $180^\circ$.

Given relationships:
  • $\angle A = 3\angle B$
  • $\angle C = 2\angle B$
Using the triangle angle sum theorem:

The sum of the angles in $\Delta ABC$ is $180^\circ$:

$ \angle A + \angle B + \angle C = 180^\circ $

Substitute the given relationships into the equation to express everything in terms of $\angle B$:

$ (3\angle B) + \angle B + (2\angle B) = 180^\circ $

Combine the terms involving $\angle B$:

$ 6\angle B = 180^\circ $

Solve for $\angle B$:

$ \angle B = \frac{180^\circ}{6} $ $ \angle B = 30^\circ $

Now, calculate $\angle A$ and $\angle C$ using the value of $\angle B$:

  • $\angle A = 3\angle B = 3 \times 30^\circ = 90^\circ$
  • $\angle C = 2\angle B = 2 \times 30^\circ = 60^\circ$

Therefore, the values of the angles are $\angle A = 90^\circ$, $\angle B = 30^\circ$, and $\angle C = 60^\circ$. This matches Option B.

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Important Questions from Lines and Angles

  1. If angles of a triangle are in the ration of 2 : 3 : 4, then the measure of the smallest angle is:

  2. In the triangle, if AB = AC and ∠ABC = 72°, then ∠BAC is:

  3. The angles of a triangle are (8x - 15)°,(6x - 11)° and ( 4x – 10)°. What is the value of x ?

  4. In a ΔABC, the bisectors of ∠B and ∠C meet at point O, inside the triangle. If ∠BOC = 122°, then the measure of ∠A is:

  5. In ΔABC, D is a point on side BC such that ∠ADC = 2∠BAD. If ∠A = 80° and ∠C = 38°, then what is the measure of ∠ADB? 

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