$\"\"$

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The average speed of the aircraft is $\"\"$ .

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The distance travelled in $\"\"$ minutes is $\"\"$ .

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(a)

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Draw the related diagram .

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$\"\"$

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Here $\"\"$ , $\"\"$ and $\"\"$ .

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Find the third side of the triangle;

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Cosine law: $\"\"$ .

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Substitute $\"\"$ , $\"\"$ and $\"\"$ .

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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 angle of the opposite side of $\"\"$ .

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Cosine law: $\"\"$ .

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Substitute $\"\"$ , $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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Therefore, the flight should turn through an angle of $\"\"$ .

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$\"\"$

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(b)

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The total time of the pilot is $\"\"$ .

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Find the new average speed.

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The plane must to travel $\"\"$ .

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The avearge speed is $\"\"$ .

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$\"\"$

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$\"\"$ .

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Therefore, the pilot must maintain a speed of $\"\"$ to complete the trip in $\"\"$ .

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$\"\"$

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(a) The flight should turn through an angle of $\"\"$ .

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(b) The pilot must maintain a speed of $\"\"$ to complete the trip in $\"\"$ .