Tell whether the lines for each pair of equations are parallel, perpendicular, or neither.
y = –2x + 4
–5x + 10y = 5
y = m x + b
if y = –2x + 4
m = slope = -2
for the second one
–5x + 10y = 5
is
-x + 2 y = 1
y = (1/2) x + 1/2
m' = 1/2
so we know m' = -1/m
which means PERPENDICULAR