$\"\"$

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(a)

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The equation is $\"\"$ .

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$\"\"$

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About this graph cosine is positive in first and fourth quadrants.

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In first quadrant :

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ . $\"\"$

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In fourth quadrant :

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ . $\"\"$

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(b)

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The equation is $\"\"$ .

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The cosine function is negative in second and third quadrants.

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In second quadrant :

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ . $\"\"$

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In third quadrant :

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ . $\"\"$

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(a) The two solutions are $\"\"$ and $\"\"$ .

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(b) The two solutions are $\"\"$ and $\"\"$ .