If (x + 1/x) = 4, then (x4 + 1/x4) is equal to :
Option:
A. 196
B. 194
C. 192
D. 190
Answer: B . 194
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Justification:
x + 1/x = 4 → ( x + 1/x)2 = 16 → x2 + 1/x2 + 2 = 16 → x2 +1/x2 = 14
Now,
x2 + 1/x2 = 14 → ( x2 + 1/x2)2 = 196 → x4 + 1/x4 + 2 = 196 → x4 +1/x4 = 194.
