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Teaching video
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Grade 4 chapters and video availability01 · Read and understand
What you will learn
- Describe a triangle by side lengths and angle types.
- Explain your method and check what the result means in the stated situation.
Before you start
Multiplication and division facts, simple fractions, place value, and basic length and area measurement.
Keep paper nearby. Read the question once for the context, then again to identify what is known and what you need to find.
Start with a question
A triangle has two equal sides and one angle greater than 90°. How should it be described?
Why this math matters
Describe shapes using multiple properties instead of relying on one visual impression. The worked example shows how to connect the situation, its mathematical representation, and a check on the result.
Set up the model
A useful answer starts with clear assumptions:
- Use the units, grouping rules, and reference whole stated in the question.
- Treat the supplied counts and measurements as exact within the classroom model, unless an estimate or a random outcome is requested.
02 · Work through the example
Follow the reasoning, one step at a time.
Try to predict the next step before reading it. After each calculation, explain why the operation makes sense and how it helps answer the original question.
Work through it with Amar
See this example unfold.
The complete worked example, one idea at a time.
Classify triangles in two ways
PausedQuestion: Start with the question. Paused.
Question
Start with the question
A triangle has two equal sides and one angle greater than 90°. How should it be described?
Before you calculate
Read what is known and what you need to find. Make a prediction before moving to the first calculation.
Starts paused. Play advances through the full text at a reading pace; pause whenever you need more time. Previous, Next, and the phase buttons let you set your own pace. Playback pauses when this walkthrough leaves the screen or you switch tabs.
Your device’s reduced-motion setting keeps each phase still. Manual controls remain available. The full written solution stays below.
Represent the situation
Two equal sides: isosceles
Side classification compares lengths.
Connect the parts
One angle above 90°: obtuse
Angle classification compares openings.
State and check the result
An obtuse isosceles triangle
Both labels apply because they answer different classification questions.
The result
An obtuse isosceles triangle
Both labels apply because they answer different classification questions.
Common mistakes to catch
- Do not confuse side categories with angle categories.
- A rough drawing may not show exact equality or angle size.
03 · Practice independently
Try it before revealing the answer.
Use paper or a calculator as needed. Write your units and reasoning, then open the hint or explanation to check your approach.
Practice 1
Can a triangle be both right and scalene?
Show a hint
Side equality and angle type are independent features.
Reveal answer and explanation
Yes
A 3–4–5 triangle has unequal sides and a right angle.
Practice 2
Can a plane triangle have two obtuse angles?
Show a hint
Two angles above ninety already exceed 180 together.
Reveal answer and explanation
No
Its three interior angles must total 180 degrees.
Take the idea with you
Describe shapes using multiple properties instead of relying on one visual impression.
04 · Reflect and continue
Can you explain it in your own words?
Before moving on, explain the main idea without looking at the worked example. Try both practice questions, check your reasoning, and name one mistake you now know how to avoid. Return to a step if you still need support.
Up next: Convert through metric length units
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