The equation of line cd is y=3x -3. write an equation of a line perpendicular to line cd in slope intercept form that contains points (3, 1)

(I'm learning this right now!)

y = 3x - 3
If a line is perpendicular to another line, they have negative reciprocal slopes.
So you would use the slope -1/3.

Use y - y₁ = m(x - x₁) to get an equation in slope intercept form.
Plug the numbers in.

y - 1 = -1/3(x - 3)
y - 1 = -1/3x + 1
y = -1/3x + 2

An equation of a line perpendicular to line CD is y = -1/3x + 2.