Is the Angular Equation Divided by Radius in This Example?

[MMCS]

attached is an example question i am working through, i would appreciate if anybody could explain to me the part in the red box.

I understand the relationship

linear acceleration = ang acceleration*radius

however, this working appears to divide the angular equation by the radius?

thanks

 

[milesyoung]

The equation just above it:
P*r = T_f + I*α

Do you understand that one?

 

[MMCS]

oh yes, of course, i assumed it was a subscript not a multiplication of radius (where the tansion force would be acting) been looking at it too long i think, thanks for your help milesyoung

 

[milesyoung]

No problem, whoever wrote the solution should have stuck to R_d.

Edit:
Also, if something seems off about the equation you're working with, try comparing the units of whatever quantity you have on the LHS and RHS. Something might be rotten in the state of Denmark.