$\"\"$

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Observe the parallelogram figure, the sides are $\"\"$ and diagonals $\"\"$ ; angles are $\"\"$ .

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In parallelogram, the supplementary angles are $\"\"$ .

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So the remaining angle is $\"\"$ .

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Apply the law of cosines to find the un known diagonal d in the figure.

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$\"\"$ (Write law of cosines)

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Use calculator)

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$\"\"$ (Simplify) $\"\"$

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Apply the law of cosines to find the un known diagonal c in the figure.

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$\"\"$ (Write law of cosines)

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Use calculator)

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$\"\"$ (Simplify) $\"\"$

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The solutions are $\"\"$ .