nnnx x a ) (01) (0x x X nnnX a1Bng php bin i ta a chui trn v dng IV. CHUI LY THA Do cc kt qu v chui ly tha ch cn xt cho trng hp chui c dng nnnx a1 hi t tiR rng chui nnnx a10 xChui ly tha l chui c dng 1.nh nghaKhong (-R, R)c gi l khong hi t ca chui ly tha 2. nh ngha bn knh hi t ca chui ly tha. S R > 0 sao cho chui ly tha nnnx a1R x x < : hi t vi mi v phn k vi mi R x x > : c gi l bn knh hi t ca chui. nnnx a1nnnx a1nnnx a1Nu chui ly tha Nu chui ly tha phn k x 0ta cho R = 0. hi t x Rta cho R = + .2. nh ngha bn knh hi t ca chui ly tha (tt). + nnnaa1limnnnx a13. Cch tm bn knh hi t ca chui ly tha. Khi bn knh hi t ca chui ly tha l:' + + < < + 0 ,0 ,1, 0Ra) nh l Abel:Gi s nnna limnnnx a1b. nh l Cauchy: khi bn knh hi t ca chui ly tha l:' + + < < + 0 ,0 ,1, 0R3. Cch tm bn knh hi t ca chui ly tha (tt).Gi s Ch : tm min hi t ca chui ly thannnx a1nnnx a1Tadavohainhltrntmbn knh hi t R.Bc 1:Khong hi tca chui ly tha ny l: -R < x < RXt s hi t ca chui ti cc u mt ca khong hi t.T ta s c c min hi t ca chui ly tha Bc 2:Bc 3:3. Cch tm bn knh hi t ca chui ly tha (tt).1 nnnx1111+ +nnaanannnVD1 Tm min hi t ca chui ly tha Ta c: Vy R = 14. Mt s v d: Khong hi t ca chui l -1