সমাধান - জ্যামিতিক ধারা

সিরিজের সাধারণ রূপ খুঁজে পেতে, প্রথম পদ: $$a=90$$ এবং সাধারণ অনুপাত: $$r=0.8$$ জ্যামিতিক সিরিজের সূত্রে প্লাগ করুন:

$$a_1=90$$

$$a_2=a_1·r^{n-1}=90\cdot {0.8}^{2-1}=90\cdot {0.8}^1=90\cdot 0.8=72$$

$$a_3=a_1·r^{n-1}=90\cdot {0.8}^{3-1}=90\cdot {0.8}^2=90\cdot 0.6400000000000001=57.60000000000001$$

$$a_4=a_1·r^{n-1}=90\cdot {0.8}^{4-1}=90\cdot {0.8}^3=90\cdot 0.5120000000000001=46.08000000000001$$

$$a_5=a_1·r^{n-1}=90\cdot {0.8}^{5-1}=90\cdot {0.8}^4=90\cdot 0.4096000000000001=36.864000000000004$$

$$a_6=a_1·r^{n-1}=90\cdot {0.8}^{6-1}=90\cdot {0.8}^5=90\cdot 0.3276800000000001=29.491200000000006$$

$$a_7=a_1·r^{n-1}=90\cdot {0.8}^{7-1}=90\cdot {0.8}^6=90\cdot 0.2621440000000001=23.59296000000001$$

$$a_8=a_1·r^{n-1}=90\cdot {0.8}^{8-1}=90\cdot {0.8}^7=90\cdot 0.20971520000000007=18.874368000000008$$

$$a_9=a_1·r^{n-1}=90\cdot {0.8}^{9-1}=90\cdot {0.8}^8=90\cdot 0.1677721600000001=15.099494400000008$$

$$a_{10}=a_1·r^{n-1}=90\cdot {0.8}^{10-1}=90\cdot {0.8}^9=90\cdot 0.13421772800000006=12.079595520000005$$