Step 1:

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Distance across river $\"\"$ has a distance $\"\"$ .

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Angles are $\"\"$ .

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Find the distance across the river.

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Draw the diagram.

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$\"\"$

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Observe the diagram,

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Here, $\"\"$ is the distance across the river.

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Sine rule is $\"image\"$ .

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Substitute $\"\"$ and $\"\"$ in the sine rule.

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$\"\"$

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Find the length of angle $\"\"$ .

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Substitute $\"\"$ in $\"image\"$ .

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$\"\"$

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Length of angle $\"\"$ is $\"\"$ .

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Step 2:

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Find length of $\"\"$ .

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Substitute $\"\"$ in the sine rule.

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$\"\"$

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Consider,

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$\"\"$

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The distance across the river $\"\"$ is $\"\"$ .

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Solution :

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The distance across the river $\"\"$ is $\"\"$ .