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Mathematics

Which of the following equations has two real and distinct roots ?

  1. 2x2 - 32x+943\sqrt{2}x + \dfrac{9}{4} = 0

  2. x2 + x - 5 = 0

  3. x2 + 3x + 222\sqrt{2} = 0

  4. 7x2 - 3x + 1 = 0

Quadratic Equations

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Answer

For an equation having real and distinct roots :

b2 - 4ac > 0

Comparing equation (1) with ax2 + bx + c, we get :

a = 2, b = 32 and c =94-3\sqrt{2} \text{ and c } = \dfrac{9}{4}

Substituting values in b2 - 4ac,

(32)24×2×94(-3\sqrt{2})^2 - 4 \times 2 \times \dfrac{9}{4}

181818 - 18

⇒ 0.

Comparing equation (2) with ax2 + bx + c, we get :

a = 1, b = 1 and c = -5.

Substituting values in b2 - 4ac,

⇒ 12 - 4 × 1 × (-5)

⇒ 1 + 20

⇒ 21.

Since, b2 - 4ac > 21.

∴ x2 + x - 5 = 0 has real and distinct roots.

Hence, Option 2 is the correct option.

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