If , then the value of is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 843
x + 1/x = 3..............(1)
On squaring both sides we get,
x2 + 1/x2 + 2 = 9
x2 + 1/x2 = 7..........(2)
on squaring both sides we get,
x4 + 1/x4+ 2 = 49
x4 + 1/x4 = 49 - 2
x4 + 1/x4 = 47........(3)
x + 1/x = 3
On cubing both sides we get,
x3 + 1/x3 + 3(3) = 27
x3 + 1/x3 = 27 - 9 = 18...........(4)
On multiplying eq (3) and (4)
(x4 + 1/x4 )(x3 + 1/x3 ) = 47 × 18
x7 + 1/x7 + x + 1/x = 846.
x7 + 1/x7 = 846 - 3 = 843.