posted by C .
Is this pair of lines parallel, perpendicular, or neither?
the slope of the first is -2/5 and the slope of the second is 5/2
notice their product is -1, so they are perpendicular.
(slopes are negative reciprocals of each other)
(to get the slope in my head I used the rule:
for Ax + By = C, slope = -A/B )
Change into the standard equation for a straight line of y = mx + b
5y = -2x+7 then divide by 5 to obtain
y=(-2/5)x + 7/5
Second equation is
multiply by -1
Lines are parallel if the slopes are equal. Lines are perpendicular if the slopes are the negative reciprocal of each other.