9. which pair of equations below represent perpendicular lines?
a) y = 7/8x + 12 and y = -8/7x – 8
b) y = 5x + 15 and y = -5x + 15
c) y = 4x + 9 and y = 4x -9
d) y = 9 and y = 18

and

Step-by-step explanation:

The product of the slopes of the perpendicular lines is -1

Option 1) and

General equation of line :

Comparing with general equation

Slope of line 1 =

Slope of line 2=

Now product of slopes =

                                      =

Since The product of the slopes of the perpendicular lines is -1

So, and represent perpendicular lines

Option 2) and  

General equation of line :

Comparing with general equation

Slope of line 1 = 5

Slope of line 2= -5

Now product of slopes =

                                      =

Since The product of the slopes of the perpendicular lines is not -1

So, and   does not represents the  perpendicular lines.

Option 3) and

General equation of line :

Comparing with general equation

Slope of line 1 = 4

Slope of line 2= 4

Now product of slopes =

                                      =

Since The product of the slopes of the perpendicular lines is not -1

So, and does not represents the  perpendicular lines.

Option 4) and

General equation of line :

Comparing with general equation

Slope of line 1 = 0

Slope of line 2=0

Now product of slopes =

                                      =

Since The product of the slopes of the perpendicular lines is not -1

So, and does not represents the  perpendicular lines.

2 5/8 is the final answer! : )