`P = (2a-1)/(3a-1) + (5-a)/(3a+1)`
`P = ((2a-1)(3a+1)+(5-a)(3a-1))/((3a-1)(3a+1))`
`P = (3a^2 + 15-6)/(9a^2 -1)`
Ta có `10a^2+5a= 3`
`=> 5a =3–10a^2`
Vậy, ta được `P=(3a^2 + 3(3-10a^2) – 6)/(9a^2 -1)`
`= (3-27a^2)/(9a^2 -1)`
`= (-3(9a^2 -1))/(9a^2 -1)`
`=-3`