Calculate Angle B in a Rhombus with 130° Interior Angle

Q: What's the difference between opposite and adjacent angles?

Opposite angles are directly across from each other (like B and D). Adjacent angles are next to each other (like B and A). In a rhombus, opposite angles are equal, adjacent angles add to 180°.

Q: Why are opposite angles equal in a rhombus?

A rhombus has parallel sides, which creates equal opposite angles. Think of it like two triangles put together - the angles that match up are the same size!

Q: Do all parallelograms have this same angle property?

Yes! All parallelograms (including rectangles, rhombuses, and squares) have equal opposite angles. It's one of their key properties.

Q: What if the diagram looks confusing?

Focus on the labels rather than the visual appearance. Look for vertices that are diagonal from each other - those are opposite angles, regardless of how the shape is drawn.

Rhombus Properties with Opposite Angles

Given the rhombus:

How much is it worth? $∢B$ ?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations

00:03 Let's find angle B.

00:06 We're given that this is angle C.

00:11 In a rhombus, opposite angles are equal.

00:17 And that's how we solve the question.

Step-by-step written solution

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Understand the problem

Given the rhombus:

How much is it worth? $∢B$ ?

Final Answer

130

Key Points to Remember

Essential concepts to master this topic

Rule: In a rhombus, opposite angles are always equal
Technique: If angle C = 130°, then angle B = 130°
Check: Verify all four angles sum to 360°: 130° + 50° + 130° + 50° = 360° ✓

Common Mistakes

Avoid these frequent errors

Confusing adjacent and opposite angles
Don't think adjacent angles in a rhombus are equal = wrong answer like 50°! Adjacent angles are supplementary (add to 180°), while opposite angles are equal. Always identify which angles are directly across from each other.

Practice Quiz

Test your knowledge with interactive questions

Look at the following rhombus:

Are the diagonals of the rhombus parallel?

FAQ

Everything you need to know about this question

What's the difference between opposite and adjacent angles?

Opposite angles are directly across from each other (like B and D). Adjacent angles are next to each other (like B and A). In a rhombus, opposite angles are equal, adjacent angles add to 180°.

Why are opposite angles equal in a rhombus?

A rhombus has parallel sides, which creates equal opposite angles. Think of it like two triangles put together - the angles that match up are the same size!

How do I find adjacent angles if I know one angle?

Subtract the given angle from 180°. If one angle is 130°, the adjacent angle is $180° - 130° = 50°$ .

Do all parallelograms have this same angle property?

Yes! All parallelograms (including rectangles, rhombuses, and squares) have equal opposite angles. It's one of their key properties.

What if the diagram looks confusing?

Focus on the labels rather than the visual appearance. Look for vertices that are diagonal from each other - those are opposite angles, regardless of how the shape is drawn.

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