Line a passes through (2, 10) and (4, 13). Line b passes through (4, 9) and (6, 12).
Line c passes through (2, 10) and (4,9).
Determine which of the lines if any are parallel or perpendicular. Explain

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since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.