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For the G.P. (1)/(27),(1)/(9),(1)/(3), ....

For the G.P. `(1)/(27),(1)/(9),(1)/(3), . . . . . .. . . . .. ,81,`
find the product of fourth term from the beginning and the fourth term from the beginning and the fourth term from the end.

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To solve the problem, we need to find the product of the fourth term from the beginning and the fourth term from the end of the given geometric progression (G.P.): \[ \frac{1}{27}, \frac{1}{9}, \frac{1}{3}, \ldots, 81 \] ### Step 1: Identify the first term and the common ratio The first term \( a \) of the G.P. is given as: \[ a = \frac{1}{27} \] To find the common ratio \( r \), we can take the second term and divide it by the first term: \[ r = \frac{\frac{1}{9}}{\frac{1}{27}} = \frac{1}{9} \times \frac{27}{1} = 3 \] ### Step 2: Identify the last term The last term \( L \) of the G.P. is given as: \[ L = 81 \] ### Step 3: Find the fourth term from the beginning The formula for the \( n \)-th term of a G.P. is given by: \[ T_n = a \cdot r^{n-1} \] To find the fourth term from the beginning (\( T_4 \)): \[ T_4 = a \cdot r^{4-1} = \frac{1}{27} \cdot 3^3 \] Calculating \( 3^3 \): \[ 3^3 = 27 \] Now substituting back: \[ T_4 = \frac{1}{27} \cdot 27 = 1 \] ### Step 4: Find the fourth term from the end To find the fourth term from the end, we can use the formula for the \( n \)-th term from the end, which is: \[ T_{n-k+1} = L \cdot \frac{1}{r^{k-1}} \] Here, \( k = 4 \) (since we want the fourth term from the end): \[ T_{n-3} = 81 \cdot \frac{1}{3^{4-1}} = 81 \cdot \frac{1}{3^3} \] Calculating \( 3^3 \): \[ 3^3 = 27 \] Now substituting back: \[ T_{n-3} = 81 \cdot \frac{1}{27} = 3 \] ### Step 5: Find the product of the two terms Now, we need to find the product of the fourth term from the beginning and the fourth term from the end: \[ \text{Product} = T_4 \cdot T_{n-3} = 1 \cdot 3 = 3 \] ### Final Answer Thus, the product of the fourth term from the beginning and the fourth term from the end is: \[ \boxed{3} \]
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