# Rutherford scattering: question about impact parameter

http://wonka.physics.ncsu.edu/~blondin/py203/HW5solns.pdf

I have a question about the solution to a problem I found online. I don't understand why the author plugs in $\theta=90$ when the question is asking about angles greater than 90.

a) What fraction...at angles greater than 90 degrees

Was he/she right in doing it this way?

the fraction of incident particles scattered through an angle greater than $\theta$ is given by . . . .
It might well be that the formula was derived by first finding the fraction scattered from $0^\circ$ up to and including $\theta$ and then that fraction taken away from $1$ to give the graction for an angle greater than $\theta$?