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Mathematics

Find the values of m for which equation 3x2 + mx + 2 = 0 has equal roots. Also, find the roots of the given equation.

Quadratic Equations

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Answer

When equation has equal roots, D = 0.

∴ b2 - 4ac = 0

Comparing 3x2 + mx + 2 = 0 with ax2 + bx + c = 0 we get,

a = 3, b = m and c = 2.

⇒ m2 - 4(3)(2) = 0

⇒ m2 - 24 = 0

⇒ m2 = 24

⇒ m = 24=±26\sqrt{24} = \pm 2 \sqrt{6}

Considering, m = 262\sqrt{6}

⇒ 3x2 + mx + 2 = 0

3x2 + 262\sqrt{6}x + 2 = 0

3x2 + 6x+6x+2\sqrt{6}x + \sqrt{6}x + 2 = 0

(3x+2)2(\sqrt{3}x + \sqrt{2})^2 = 0

(3x+2)(\sqrt{3}x + \sqrt{2}) = 0

x = 23-\dfrac{\sqrt{2}}{\sqrt{3}}.

Rationalising,

x=23×33=63x = -\dfrac{\sqrt{2}}{\sqrt{3}} \times \dfrac{\sqrt{3}}{\sqrt{3}} = - \dfrac{\sqrt{6}}{3}.

Considering, m = -262\sqrt{6}

⇒ 3x2 + mx + 2 = 0

⇒ 3x2 - 262\sqrt{6}x + 2 = 0

(3x2)2(\sqrt{3}x - \sqrt{2})^2 = 0

(3x2)(\sqrt{3}x - \sqrt{2}) = 0

⇒ x = 23\dfrac{\sqrt{2}}{\sqrt{3}}.

Rationalising,

x=23×33=63x = \dfrac{\sqrt{2}}{\sqrt{3}} \times \dfrac{\sqrt{3}}{\sqrt{3}} = \dfrac{\sqrt{6}}{3}.

Hence, m = ±26\pm 2\sqrt{6} and roots = ±63\pm \dfrac{\sqrt{6}}{3}.

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