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The roots of the equation 2x2−32x+c=0\sqrt{2}x^2 - \frac{3}{\sqrt{2}}x + c = 0 are pp and 2p2p.

Let a>0a > 0, and one root of the equation a2x2+12a−7=0a^2x^2 + 12a - 7 = 0 is 64(p6+c12)64(p^6 + c^{12}).

What is the value of aa?

Solution

✅ Correct Option: 2

The equation 2x2−32x+c=0\sqrt{2}x^2 - \frac{3}{\sqrt{2}}x + c = 0 has roots pp and 2p2p.

Using Vieta's formulas (relationships between roots and coefficients):

RelationshipFormulaSubstitution
Sum of rootsp+2p=3/22p + 2p = \frac{3/\sqrt{2}}{\sqrt{2}}3p=323p = \frac{3}{2}
Product of rootsp⋅2p=c2p \cdot 2p = \frac{c}{\sqrt{2}}2p2=c22p^2 = \frac{c}{\sqrt{2}}

From the sum: 3p=323p = \frac{3}{2} gives us p=12p = \frac{1}{2}

From the product: 2p2=c22p^2 = \frac{c}{\sqrt{2}}

Substituting p=12p = \frac{1}{2}:

2⋅(12)2=c22 \cdot \left(\frac{1}{2}\right)^2 = \frac{c}{\sqrt{2}}

2⋅14=c22 \cdot \frac{1}{4} = \frac{c}{\sqrt{2}}

12=c2\frac{1}{2} = \frac{c}{\sqrt{2}}

c=22=12c = \frac{\sqrt{2}}{2} = \frac{1}{\sqrt{2}}


Now we calculate 64(p6+c12)64(p^6 + c^{12}):

p6=(12)6=164p^6 = \left(\frac{1}{2}\right)^6 = \frac{1}{64}

c12=(12)12=1(2)12=1(21/2)12=126=164c^{12} = \left(\frac{1}{\sqrt{2}}\right)^{12} = \frac{1}{(\sqrt{2})^{12}} = \frac{1}{(2^{1/2})^{12}} = \frac{1}{2^6} = \frac{1}{64}

Therefore: 64(p6+c12)=64(164+164)=64⋅264=264(p^6 + c^{12}) = 64\left(\frac{1}{64} + \frac{1}{64}\right) = 64 \cdot \frac{2}{64} = 2


So one root of the equation a2x2+12a−7=0a^2x^2 + 12a - 7 = 0 is x=2x = 2.

Substituting x=2x = 2 into the equation:

a2(2)2+12a−7=0a^2(2)^2 + 12a - 7 = 0

4a2+12a−7=04a^2 + 12a - 7 = 0

Using the quadratic formula where A=4A = 4, B=12B = 12, C=−7C = -7:

a=−12±144+1128=−12±2568=−12±168a = \frac{-12 \pm \sqrt{144 + 112}}{8} = \frac{-12 \pm \sqrt{256}}{8} = \frac{-12 \pm 16}{8}

This gives: a=48=12a = \frac{4}{8} = \frac{1}{2} or a=−288=−72a = \frac{-28}{8} = -\frac{7}{2}

Since a>0a > 0, we have a=12a = \frac{1}{2}

Answer: Option 2

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