Fun of Quadratic

Algebra Level 2

Find the quadratic equation ?

Such that α \alpha and β \beta are roots

and geometric mean is 3 \sqrt{3} harmonic mean is 1.5

none of this x 2 x^{2} + 4 x 4x +3 x 2 x^{2} - 3 x 3x +4 x 2 x^{2} - 4 x 4x +3

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2 solutions

The quadratic is ( x α ) ( x β ) = x 2 ( α + β ) x + α β \color{#D61F06}{(x-\alpha)(x-\beta)=x^2-(\alpha+\beta)x+\alpha\beta} .The geometric mean is 3 = α β α β = 3 \color{rubinered}{\sqrt{3}=\sqrt{\alpha\beta}\rightarrow \alpha\beta=3} .The harmonic mean is 2 1 α + 1 β = 3 2 1 α + 1 β 2 = 2 3 α + β α β = 4 3 α + β 3 = 4 3 α + β = 4 \color{#3D99F6}{\frac{2}{\frac{1}{\alpha}+\frac{1}{\beta}}=\frac{3}{2}\rightarrow \frac{\frac{1}{\alpha}+\frac{1}{\beta}}{2}=\frac{2}{3}\rightarrow \frac{\alpha+\beta}{\alpha\beta}=\frac{4}{3}\rightarrow \frac{\alpha+\beta}{3}=\frac{4}{3}\rightarrow \alpha+\beta=4} .So the quadratic is x 2 4 x + 3 \color{#20A900}{x^2-4x+3}

Mitesh Warang
Jul 11, 2014

α \alpha β \beta =3

α \alpha + β \beta =4

Therefore x 2 x^{2} -4 x x +3

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