Will be the graphs of each of these equations be perpendicular.

Question

1.y=7x-9
slope=-7
y-intercept=-9

2.-3y=21x+7
y=-7x(7/3)
slope=-7
y-intercept=-(7/3)

Answer 1

They are perpendicular if the product of their slopes is -1.

So, is (-7)(-7) = -1 ?