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Question:-
If x - 1/x = 10 (where x is a positive integer) then find;
a) x² + 1/x²
b) x + 1/x
c) x² - 1/x²
Answer:-
1) Given:-
x - 1/x = 10
On squaring both sides we get,
⟹ (x - 1/x)² = (10)²
using (a - b)² = a² + b² - 2ab we get,
⟹ x² + 1/x² - 2(x)(1/x) = 100
⟹ x² + 1/x² = 100 + 2
⟹ x² + 1/x² = 102
∴ The value of x² + 1/x² is 102.
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2) We have;
x² + 1/x² = 102
We know,
a² + b² = (a + b)² - 2ab
So,
⟹ x² + 1/x² = (x + 1/x)² - 2(X)(1/X)
⟹ 102 = (x + 1/x)² - 2
⟹ 102 + 2 = (x + 1/x)²
⟹ 104 = (x + 1/x)²
⟹ √104 = (x + 1/x)
⟹ 2√26 = x + 1/x
∴ The value of x + 1/x is 2√26.
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3) We have;
x + 1/x = 2√26 -- equation (1)
x - 1/x = 10 -- equation (2)
Multiply equations (1) & (2).
⟹ (x + 1/x)(x - 1/x) = (2√26)(10)
using (a + b)(a - b) = a² - b² we get;
⟹ x² - 1/x² = 20√26
∴ The value of x² - 1/x² is 20√26.
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