Geometrik progressiyaning dastlabki n ta hadining yig’indisi
Dars mavzusi : « Geometrik progressiyaning dastlabki n ta hadining yig’indisi »
1-misol: Ushbu yig’indini toping. Tenglikning ikkala qismini 3 ga ko’paytiramiz. 5 4 3 2 3 3 3 3 3 1 S 6 5 4 3 2 3 3 3 3 3 3 3 S Tengliklarni bunday yozib chiqamiz. ) 3 3 3 3 3( 1 5 4 3 2 S 6 5 4 3 2 3)33333(3 S Qavsdagi ifodalar bir xil. Shuning uchun pastdagi tenglikdan yuqoridagi tenglikni ayirib , hosil qilamiz. 1 3 3 6 S S 1 3 2 6 S 364 2 1 729 2 1 3 6 S 5 4 3 2 3 3 3 3 3 1 S 6 5 4 3 2 3 3 3 3 3 3 3 S ) 3 3 3 3 3( 1 5 4 3 2 S 6 5 4 3 2 3 ) 3 3 3 3 3( 3 S 1 3 3 6 S S 1 3 2 6 S 364 2 1 729 2 1 3 6 S
Maxraji bo’lgan ixtiyoriy geometrik progressiyaning qaraymiz. Shu progressiyaning n ta hadining yig’indisini topaylik, Teorema. Maxraji bo’lgan geometrik progressiyaning dastlabki n ta hadining yig’indisi quyidagiga teng. 1 1 2 1 1 1 ... n n q b q b q b b S q q b S n n 1 ) 1(1 1 q n b b b b ..., , , , 3 2 1 1 q indisi yig hadining n dastlabki S n ' hadi birinchi b 1 xraji ma q 1 12 111 ... n n q b q b q b b S q q b S n n 1 ) 1(1 1 q n b b b b ..., , , , 3 2 1 1 q indisi yig hadining n dastlabki S n ' hadi birinchi b 1 xraji ma q
Isbot: Tenglikning ikkala qismini q ga ko’paytiramiz. Yuqoridagi ikkala tenglikdan bir xil qo’shiluvchilarni ajratib yozib chiqamiz.1 1 2 1 1 1 ... n n q b q b q b b S n n q b q b q b q b qS 1 3 1 2 1 1 ... ) ... ( 1 1 2 1 1 1 n n q b q b q b b S n n n q b q b q b q b q b qS 1 1 1 3 1 2 1 1 ) ... ( Qavs ichida turgan ifodalar teng. Shuning uchun yuqoridagi tenglikdan pastdagisini ayirib, hosil qilamiz. n n n q b b qS S 1 1 ) 1( ) 1( 1 n n q b q S q q b S n n 1 ) 1(1 1 12 111 ... n n q b q b q b b S n n q b q b q b q b qS 1 3 1 2 1 1 ... ) ... ( 1 1 2 1 1 1 n n q b q b q b b S n n n q b q b q b q b q b qS 1 1 1 3 1 2 1 1 ) ... ( n n n q b b qS S 1 1 ) 1( ) 1( 1 n n q b q S q q b S n n 1 ) 1(1
2-misol: geometrik progressiya dastlabki beshta hadining yig’indisini hisoblang. ..., 3 2 , 2 , 6 Bu progressiyada 31 ,6 1 qb 27 242 243 2 3 242 6 3 2 243 1 1 6 3 1 1 3 1 1 6 1 ) 1( 5 5 1 5 q q b S ..., 3 2 , 2 , 6 3 1 , 6 1 q b 27 242 243 2 3 242 6 3 2 243 1 1 6 3 1 1 3 1 1 6 1 ) 1( 5 5 1 5 q q b S