Question

Which of the following is an equation of a curve that intersects at right angles every curve of the family y=(1/x)+k (where k takes all real values)?
a. y=-x
b. y=-x^2
c. y=(-1/3)x^3
d. y= (1/3)x^3
e. y=lnx

Answer 1

If you set the equations equal to each other, you can find common points.

Answer 2

So, it should be d. :)