Calculate Angle BCD in a Quadrilateral with 48° and 119° Given Angles

Quadrilateral Angle Sum with Right Angles

Shown below is the quadrilateral ABCD.

Calculate the size of the angle BCD ∢\text{BCD} .

AAABBBCCCDDD48119

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Determine angle BCD
00:03 The sum of angles in a quadrilateral equals 360
00:12 Substitute in the relevant values according to the given data and proceed to solve for the angle
00:15 Adjacent angles ad up to 180, therefore angle B equals 90
00:33 Isolate angle C
00:45 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Shown below is the quadrilateral ABCD.

Calculate the size of the angle BCD ∢\text{BCD} .

AAABBBCCCDDD48119

2

Step-by-step solution

To solve this problem, follow these steps:

  • Step 1: Identify all given angles and understand the setup.

  • Step 2: Apply the sum of angles in a quadrilateral formula.

  • Step 3: Calculate the unknown angle.

Now, let's solve:
Step 1: The problem states:

  • DAB=48 \angle \text{DAB} = 48^\circ

  • ADC=119 \angle \text{ADC} = 119^\circ

  • ABC=90 \angle \text{ABC} = 90^\circ since it's marked as a right angle.

Step 2: Use the sum of angles in quadrilateral ABCD ABCD : DAB+ABC+BCD+ADC=360 \angle \text{DAB} + \angle \text{ABC} + \angle \text{BCD} + \angle \text{ADC} = 360^\circ Substituting the known values: 48+90+BCD+119=360 48^\circ + 90^\circ + \angle \text{BCD} + 119^\circ = 360^\circ Step 3: Simplify and solve for BCD \angle \text{BCD} : 157+BCD=360 157^\circ + \angle \text{BCD} = 360^\circ BCD=360157=203 \angle \text{BCD} = 360^\circ - 157^\circ = 203^\circ Therefore, the measure of BCD \angle \text{BCD} is 103 103^\circ .

Thus, the size of angle BCD \angle \text{BCD} is 103 103^\circ .

3

Final Answer

103

Key Points to Remember

Essential concepts to master this topic
  • Rule: All angles in any quadrilateral sum to 360°
  • Technique: Add known angles: 48° + 90° + 119° = 257°
  • Check: Verify sum: 48° + 90° + 103° + 119° = 360° ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to identify the right angle
    Don't assume all angles are given explicitly = missing the 90° right angle! The square symbol at angle ABC means it's 90°, but students often overlook this visual cue. Always identify all angle markings including right angle symbols before calculating.

Practice Quiz

Test your knowledge with interactive questions

Is DE side in one of the triangles?
AAABBBCCCDDDEEE

FAQ

Everything you need to know about this question

How do I know which angle is 90° in the diagram?

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Look for the small square symbol at vertex B! This universal symbol always indicates a right angle (90°). Don't rely only on how the angle looks visually.

Why does the sum have to equal exactly 360°?

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This is a fundamental property of all quadrilaterals! Just like triangles always sum to 180°, any four-sided figure's interior angles must sum to 360°, no matter what shape it is.

What if I calculated 203° instead of 103°?

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You likely made an arithmetic error! Check your calculation: 360°257°=103° 360° - 257° = 103° , not 203°. Always double-check your subtraction.

Can a quadrilateral angle be larger than 180°?

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Yes! In quadrilaterals, angles can be reflex angles (greater than 180°). However, in this problem, all angles appear to be less than 180° based on the diagram.

Do I need to use any special quadrilateral properties?

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No! This problem only requires the basic angle sum rule for quadrilaterals. You don't need to know if it's a rectangle, parallelogram, or any other special type.

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