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0.6
6/10.
Class 9 · Bangla Version · Mathematics
Geometry, measurement and trigonometry readiness
Use right-triangle trigonometry and similar-shape scaling.
About this lesson and its coverage
Original Kidemy Class 9 progression. This level has its own text, examples and questions. Curriculum versions share the progression; complete board-specific coverage still needs specification matching and additional material.
Learn the idea
Choose the angle first, then label opposite, adjacent and hypotenuse. The sine ratio is opposite/hypotenuse; cosine is adjacent/hypotenuse. These side ratios apply to right triangles. Check angle units in a calculator.
Worked example
If sinθ=3/5 in a right triangle, an opposite side 6 corresponds to hypotenuse 10. Similar-shape area ratios use squared length ratios.
- Identify the quantities and restrictions.
- Show a method with units or symbols.
- Check and explain the result.
Your written practice
Show your working on paper. Check your answer, then choose Next.
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4
Area ratio 4:25.
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78.5
3.14×25.
Write in your own words. A guardian or teacher should review this response.
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It divides two lengths with the same unit, so units cancel.
Explain the dimensionless comparison.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
√(10²−8²)=6m.
State the right-angle condition.
Progress and browser storage
Notebook challenge, sources and further study
Apply the idea
Draw a right-triangle model, choose a ratio and check a length by Pythagoras.
Review with a guardian or teacher
- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
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