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OT:a.Z of an hour =b. 5 of 3 72 = 3minutesC.3 4of 72 kggd.of 12 litres6MLe9 of 42 secondsseconds7tros |
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Answer» GIVEN : x = √5 + 2 To find : x² + 1 / x² Solution : x = √5 + 2 ⇒ 1 / x = 1 / √5 + 2 ⇒ 1 / x = 1 / √5 + 2 × √5 - 2 / √5 - 2 ⇒ 1 / x = √5 - 2 / ( √5 )² - ( 2 ) ² ⇒ 1 / x = √5 - 2 / 5 - 4 ⇒ 1 / x = √5 - 2 Now, x + 1 / x = √5 + 2 + √5 - 2 x + 1 / x = 2 √5 Again, On SQUARING both sides, we have ; ( x + 1 / x )² = ( 2 √5 ) ² ⇒ x² + 1 / x² + 2 = 20 ⇒ x² + 1 / x² = 20 - 2 ⇒ x² + 1 / x² = 18 Hence, The value of x² + 1 / x² = 18. |
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