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Need to prove the area of sector of a circle with radius $\"\"$ and central angle $\"\"$ .

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The circle equation is $\"\"$ .

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Find the $\"\"$ in terms of $\"\"$ .

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Observe the figure: $\"\"$ triangle is right angle triangle.

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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Find the area of the triangle $\"\"$ :

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Area of the triangle $\"\"$ .

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Triangle $\"\"$ base is $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$ .

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Find the area of the region $\"\"$ :

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Area of the shaded region $\"\"$ .

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Apply the formula : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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The area of sector of a circle with radius $\"\"$ and central angle $\"\"$ , $\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$ .