Line L1 passes through the points (2, a) and (5, 6). Line L2 passes through the points (4, 1) and (10, 5). If L1 is parallel to L2, what is the value of a?
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Correct answer: A
Explanation
L1: (2, a), (5, 6)
L2: (4, 1), (10, 5)
Parallel lines ⇒ Slopes are equal
Slope of L1 = (6 − a)/(5 − 2) = (6 − a)/3
Slope of L2 = (5 − 1)/(10 − 4) = 4/6 = 2/3
⇒ (6 − a)/3 = 2/3
⇒ 6 − a = 2
⇒ a = 4