R2+3RA+2A2,
R2+RA+2RA+2A2, (open out the middle term, trying to duplicate the coefficients of R2 and A2)
R(R+A)+2A(R+A), (factorise by noticing common factors).
R+A becomes a new common factor so it can be isolated and distributed:
(R+2A)(R+A) is the final factorisation.