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Answers
Step-by-step explanation:
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Question :-
If x + 1/x = p, then value of x - 1/x is :
(a) p² - 4
(b) p² + 4
(c) √( p² + 4 )
(d) √( p² - 4 )
Answer :-
(d) √( p² - 4 )
Explanation :-
x + 1/x = p
Squaring on both sides
⇒ (x + 1/x)² = p²
⇒ (x)² + (1/x)² + 2(x)(1/x) = p²
[ Because (a + b)² = a² + b² + 2ab ]
⇒ x² + (1/x)² + 2 = p²
⇒ x² + (1/x)² = p² - 2
Subtracting 2 on both sides
⇒ x² + (1/x)² - 2 = p² - 2 - 2
⇒ x² + (1/x)² - 2(x)(1/x) = p² - 4
[ Because (a - b)² = a² + b² - 2ab ]
⇒ (x - 1/x)² = p² - 4
Taking square root on both sides
⇒ x - 1/x = √( p² - 4 )
Another way
We know that
(a - b)² = (a + b)² - 4ab
Here
• a = x
• b = 1/x
By substituting the values
⇒ (x - 1/x)² = (x + 1/x)² - 4(x)(1/x)
⇒ (x - 1/x)² = p² - 4
[ Because x + 1/x = p ]
Taking square root on both sides
⇒ x - 1/x = √( p² - 4 )