If x + y = 12 and xy = 27, x > y, then the value of (x3-y3) is:
Show answer & explanation
Correct answer: D
Explanation
Correct Answer is option 4 i.e. 702
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Concept |
Understanding |
Application |
Fair calculation |
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(x – y)2 = (x + y)2 – 4xy |
x + y = 12 and xy = 27, x > y |
(x – y)2 = 144 – 4 × 27 = 144 – 108 = 36 x – y = 6 And (x + y)2 = 144 x2 + y2 + 2xy = 144 x2 + y2 = 144 – (2 × 27) = 90 Now x3 – y3 = (x – y)(x2 + y2 + xy) = 6 × (90 + 27) = 6 × 117 = 702 |
144 – 4 × 27 = 144 – 108 = 36
144 – (2 × 27) = 144 – 54 = 90 |