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Question

The measure of an angle is one half of its supplementary angle. Find its measure.

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

Angle Measure Calculation

Setting Up the Supplementary Angle Equation

Let the measure of the unknown angle be $x$.

Two angles are supplementary if their sum is $180^{\circ}$. Therefore, the supplementary angle to $x$ measures $180^{\circ} - x$.

The problem states that the measure of the angle ($x$) is one half of its supplementary angle ($180^{\circ} - x$). This can be written as an equation:

$x = \frac{1}{2} (180^{\circ} - x)$

Solving for the Angle

To find the measure of the angle, we solve the equation:

  1. Multiply both sides of the equation by 2 to eliminate the fraction:

    $2 \times x = 2 \times \frac{1}{2} (180^{\circ} - x)$

    $2x = 180^{\circ} - x$

  2. Add $x$ to both sides of the equation to gather the terms involving $x$ on one side:

    $2x + x = 180^{\circ} - x + x$

    $3x = 180^{\circ}$

  3. Divide both sides by 3 to isolate $x$:

    $x = \frac{180^{\circ}}{3}$

    $x = 60^{\circ}$

Thus, the measure of the angle is $60^{\circ}$.

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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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