Quadratic Equation
- The sum of a number and its reciprocal is 10/3, then the numbers are
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Let the number be x and 1/x,
Then, x + 1/x = 10/3
⇒ x2 + 1/x = 10/3Correct Option: A
Let the number be x and 1/x,
Then, x + 1/x = 10/3
⇒ (x2 + 1)/x = 10/3
⇒ 3x2 - 10x + 3 = 0
⇒ 3x2 - 9x - x + 3 = 0
⇒ 3x(x - 3) -1 (x - 3) = 0
⇒ (3x - 1) (x - 3) = 0
∴ x = 1/3, x = 3
- The values of p for which the difference between the roots of the equation x2 + px + 8 = 0 is 2 , are
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α + β = - p, α β = 8
Given, α - β = 2
On squaring both sides, we get
(α - β)2 = 4Correct Option: C
α + β = - p, α β = 8
Given, α - β = 2
On squaring both sides, we get
(α - β)2 = 4
⇒ (α + β)2 - 4αβ = 4
⇒ p2 - 32 = 4
⇒ p2 = 36 ⇒ p = ± 6
Direction: In each of the following question, there are two equations. you have to solve both equations and give answer.
- x2 + x - 20 = 0
y2 - y - 30 = 0
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x2 + x - 20 = 0
[by factorisation method]
(x + 5) (x - 4) = 0
and y2 - y - 30 = 0
⇒ (y - 6) (y + 5) = 0Correct Option: D
x2 + x - 20 = 0
[by factorisation method]
⇒ x2 + 5x - 4x - 20 = 0
⇒ x(x + 5) - 4(x + 5) = 0
(x + 5) (x - 4) = 0
∴ x = -5 or 4
and y2 - y - 30 = 0
⇒ y2 - 6y + 5y - 30 = 0
⇒ y(y - 6) + 5(y - 6) = 0
⇒ (y - 6) (y + 5) = 0
∴ y = 6 or - 5
Hence, y ≥ x or x ≤ y
- If x2 - 3x + 1 = 0, find the value of x + 1/x,
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Given equation is
x2 - 3x + 1 = 0 ⇒ x2 + 1 = 3x
⇒ x2 + 1/x = 3
⇒ x2/x + 1/x = 3
∴ x + 1/x = 3Correct Option: B
Given equation is
x2 - 3x + 1 = 0 ⇒ x2 + 1 = 3x
⇒ x2 + 1/x = 3
⇒ x2/x + 1/x = 3
∴ x + 1/x = 3
- x - √121 = 0
y2 - 121 = 0
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x - √121 = 0
⇒ x = √121 ⇒ x = ± 11
and y2 - 121 = 0 ⇒ y2 = 121
⇒ y = √121 = ± 11
∴ x = yCorrect Option: E
x - √121 = 0
⇒ x = √121 ⇒ x = ± 11
and y2 - 121 = 0 ⇒ y2 = 121
⇒ y = √121 = ± 11
∴ x = y