SOLUTION: Determine which two equations represent parallel lines. a)y=-9x+4 b)y=9x+4 c)y=1/9x+4 d)y=-9x+5

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To determine if lines are parallel, you must know their slopes and decide which lines have the SAME SLOPE. In this case, the lines are all given in slope-intercept form, so the slopes is just the coefficients of x.

A) m=-9
B) m=9
C) m=1/9
D) m=-9

The two slopes that are EQUAL are A) and D), so these lines are PARALLEL!!

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