$\"\"$

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The formula $\"\"$ hours.

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(a) Summer solstice $\"\"$ , equator $\"\"$ .

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Substitute $\"\"$ and $\"\"$ in day function $\"\"$ .

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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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(b) Vernal equinox $\"\"$ , equator $\"\"$ .

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Substitute $\"\"$ and $\"\"$ in day function $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$

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(c) July 4 $\"\"$ , equator $\"\"$ .

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Substitute $\"\"$ and $\"\"$ in day function $\"\"$ .

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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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(d) It $\"\"$ s always $\"\"$ 12 of day light because at the equator, $\"\"$ .

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Substitute $\"\"$ in day function $\"\"$ .

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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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(a) On Summer solstice is $\"\"$ .

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(b) On Vernal equinox is $\"\"$ .

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(c) On July 4 is $\"\"$ .

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(d) $\"\"$ .