Respuesta :

Use formula: (a-b)² = a² - 2ab + b²

(r-1)
² = r² - 2r + 1
(r-1)^2= (r-1)(r-1)

Foil:

First: r*r=r^2
Outer: r*-1= -r
Inner: r*-1= -r
Last: -1*-1= 1

Put it together and simplify:
r^2-r-r+1
r^2-2r+1

Final answer: r^2-2r+1