67.2 Agar arifmetik progressiyaning dastlabki n ta hadining yig’indisi formula bilan topilsa, uning umumiy hadi qanday ifodalanadi?
68. (an) ketma-ketlikning dastlabki n ta hadining yig’indisi formula bo’yicha hisoblanadi. ning qiymatini toping.
69.Arifmetik progressiyada va bo’lsa, ayirmani toping.
70. Arifmetik progressiyada va d=–4 bo’lsa, a25 ning qiymatini toping.
71. Agar arifmetik progressiyada bo’lsa, uning hadlari ayirmasi qanchaga teng bo’ladi?
72. Dastlabki yettita hadining yig’indisi 126 ga, dastlabki sakkizta hadining yig’indisi 164 ga va hadlarining ayirmasi 5 ga teng bo’lgan arifmetik progressiyaning birinchi hadini toping.
72.1 Dastlabki yettita hadining yig’indisi –266 ga, dastlabki sakkizta hadining yig’indisi –312 ga va hadlarining ayirmasi –2 ga teng bo’lgan arifmetik progressiyaning birinchi hadini toping
73. Arifmetik progressiyada a3+a5=12. S7 ni toping.
73.1 Arifmetik progressiyada a2+a8=12. S9 ni toping.
73.2 Arifmetik progressiyada a4+a9=8. S12 ni toping.
74. Ikkinchi va o’n to’qqizinchi hadlarining yig’indisi 12 ga teng bo’lgan arifmetik progressiyaning dastlabki yigirmata hadining yig’indisini toping.
75. Arifmetik progressiyada bo’lsa, uning dastlabki 19 ta hadlari yig’indisini toping.
75.1 Arifmetik progressiyada bo’lsa, uning dastlabki 31 ta hadlari yig’indisini toping.
76. Arifmetik progressiyada a4+a6=10. S9 ni toping.
77. Arifmetik progressiyada . Shu progressiyaning dastlabki 20 ta hadlari yig’indisini toping.
