Gulnara D. Amanova, Aigul U. Abdrahmanova, Bibigul Zh. Akimova, Kunsulu Zh. Saduakassova, Gauhar Zh. Zhumabekova, Assem A. Kazhmukhametova
INT ELECT J MATH ED, Volume 11, Issue 9, 2016, 3197-3202