Question 128

If thew first and sixth terms of geometric progessions are $$\frac{2}{3}$$ and 162 respectively then the $$8^{th}$$ term of the progression is

let the first term is a and common ratio is r then

$$T_{1}$$= {a}$$\times{r}^{1-1}$$ = a =Β Β $$\frac{2}{3}$$Β Β  Β  Β  Β  Β  Β  Β  Β equation 1

$$T_{6}$$= {a}$$\times{r}^{6-1}$$ =Β {a}$$\times{r}^{5}$$ = 162Β Β  Β  Β equation 2

equation 1 \equation 2

$$\frac{2}{3}$$\162 = 1\r^5

243 = r^5

3 = r

r = 3Β 

put the value of a andΒ  r in equation following equationΒ 

$$T_{8}$$= {a}$$\times{r}^{8-1}$$ =Β  $$\frac{2}{3}$$Β $$\times{3}^{7}$$Β 
Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β $$T_{8}$$Β  Β  Β  Β  Β =Β Β  $$\frac{2}{3}$$Β $$\times243$$Β $$\times3$$Β $$\times3$$Β Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β Β 

Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  Β  $$T_{8}$$Β  Β  Β  Β  = 1458Β  Β  Β AnswerΒ 

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