Slopes of perpendicular lines

If two lines in the standard (x,y) coordinate plane are perpendicular, and the slope of one of the lines is -5/7, what is the 
slope of the other line ?
A.)  7/5
B.)  5/7
C.)  -5/7
D.)  -7/5
​E.)  -5

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Perpendicular lines have slopes which are negative reciprocals of each other.  For example:  3/4  and  -4/3.

Parallel lines have equal slopes.

If the slope of one of the perpendicular lines is -5/7,
the slope of the other line would be 7/5.   {the negative reciprocal of -5/7}

A.)  7/5

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