If x x2 - 4 x + 1 = 1 9 , then the value x3 + 1 x3 .
Options
729
1256
1839
2158
Correct Answer :
Solution :
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The correct option is 2158.
Step 1: Simplify the given algebraic equation.
We are given:
x x2 - 4 x + 1 = 1 9
Taking the reciprocal on both sides (since x ≠ 0):
x2 - 4 x + 1 x = 9
Dividing each term in the numerator by x:
x - 4 + 1 x = 9
Adding 4 to both sides gives:
x + 1 x = 13
Step 2: Calculate the required expression.
We use the algebraic identity for the cube of a binomial:
( x + 1 x ) 3 = x3 + 1 x3 + 3 ( x + 1 x )
Substituting x + 1 x = 13 into the identity:
133 = x3 + 1 x3 + 3 ( 13 )
2197 = x3 + 1 x3 + 39
Subtracting 39 from both sides:
x3 + 1 x3 = 2197 - 39 = 2158
Thus, the value of the expression is 2158.
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