If x + y = 7 and xy = 10, then the value of (1/x3 + 1/y3) is:
Show answer & explanation
Correct answer: B
Explanation
Correct Answer is option 2 i.e. 0.133
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Concept |
Understanding |
Application |
Fair calculation |
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x3 + y3 = (x + y) (x2 + y2 – xy)
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Given x + y = 7 xy = 10 |
1/x3 + 1/y3 = [x3 + y3]/x3y3 = [(x + y) (x2 + y2 – xy)]/x3y3 = [(x + y) ((x + y)2 – 3xy)]/x3y3 = [7((7)2 – 30)]/1000 = 133/1000 = 0.133 |
[7((7)2 – 30)]/1000 = [7(49 – 30)]/1000 = [7 × 19]/1000 = 133/1000 = 0.133 |