The product of three consecutive terms of a G.P. is 512. If 4 is added...
The product of three consecutive terms of a G.P. is 512. If 4 is added...
Given:
The product of three consecutive terms of a geometric progression (G.P.) is 512.
To find:
The sum of the original three terms of the given G.P.
Solution:
Let the three consecutive terms of the G.P. be a/r, a, and ar, where 'a' is the first term and 'r' is the common ratio.
The product of these three terms is given by:
(a/r) * a * (ar) = 512
Simplifying the above expression, we get:
a^3 = 512
Taking the cube root on both sides, we get:
a = 8
So, the three terms of the G.P. are 8/r, 8, and 8r.
Adding 4 to the first and second terms:
The new terms become (8/r) + 4, 8 + 4, and 8r.
Forming an arithmetic progression (A.P.):
The three terms now form an arithmetic progression. This means that the difference between any two consecutive terms is constant.
The difference between the second and first term is:
(8 + 4) - ((8/r) + 4) = 8 - (8/r) = 8r - (8/r)
The difference between the third and second term is:
(8r) - (8 + 4) = 8r - 12
Since the difference between any two consecutive terms is constant, we equate the two expressions for the difference and solve for 'r':
8r - (8/r) = 8r - 12
Simplifying the above expression, we get:
8 - (8/r) = -12
Multiply both sides by 'r' to eliminate the fraction:
8r - 8 = -12r
Rearranging the terms, we get:
20r = 8
Dividing both sides by 20, we get:
r = 2/5
Substituting the value of 'r' back into the terms:
The three terms of the A.P. are (8/2/5) + 4, 8 + 4, and (8 * 2/5).
Simplifying the terms, we get:
(40/2) + 4, 12, and (16/5)
The sum of these three terms is:
(40/2) + 4 + 12 + (16/5) = 20 + 4 + 12 + (16/5) = 48 + (16/5)
Converting the mixed fraction to an improper fraction, we get:
48 + (16/5) = (240/5) + (16/5) = (240 + 16)/5 = 256/5
Therefore, the sum of the original three terms of the given G.P. is 256/5, which is approximately equal to 51.2.
Hence, option D is the correct answer.