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

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Can a triangle have a right angle?

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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