What is the equation of the perpendicular bisector of the segment joining points a(1, 1) and b(5, 7)?

Bisector must pass through the mid-point, so we have to find out that mid-point of the segment:

mid point = x₁+x₂ / 2 , y₁+y₂/2
= 1 + 5 / 2 , 1 + 7 / 2
= 6/2 , 8/2
= (3, 4)

Slope of given segment = m = y₂-y₁ / x₂- x₁
m = 7-1 / 5-1
m = 6/4
m = 3/2

Now, segment which is perpendicular, will have the opposite & reciprocal slope, So, it would be: -2/3

We know, y - y₁ = m(x - x₁)
y - 4 = -2/3(x - 3)
y - 4 = -2/3x + 2
y = -2/3x + 6

In short, Your Final Answer would be: y = -2/3x + 6

Hope this helps!