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​If α and β where α > β. are the roots of the equation 5x² – 3x – 2 = 0, then what is the value of (α – 2β) ?
Question

​If α and β where α > β. are the roots of the equation 5x² – 3x – 2 = 0, then what is the value of (α – 2β) ?

A.

95\frac{9}{5}​​

B.

15\frac{1}{5}​​

C.

75\frac{7}{5}​​

D.

115\frac{11}{5}​​

Correct option is A

Given:
Equation: 5x23x2=05x^2 - 3x - 2 = 0​​

Formula Used: 

For a quadratic equation ax2+bx+c=0,ax^2 + bx + c = 0,​​
Sum of roots (α+β) = ba-\frac {b}{a}​, Product of roots (αβ) = ca\frac {c}{a} 

(αβ)2=(α+β)24αβ(\alpha - \beta)^2 = (\alpha + \beta)^2 - 4\alpha \beta 

α2β=(αβ)β\alpha - 2\beta = (\alpha - \beta) - \beta​​

Solution: 

5x23x2=05x^2 - 3x - 2 = 0​​
here, a = 5, b = -3, c = -2: 

So, 

α+β=(3)5=35,αβ=25\alpha + \beta = \frac{-(-3)}{5} = \frac{3}{5}, \quad \alpha \beta = \frac{-2}{5}​​

(αβ)2=(35)24(25)(\alpha - \beta)^2 = \left( \frac{3}{5} \right)^2 - 4\left( -\frac{2}{5} \right)​​

=925+85= \frac{9}{25} + \frac{8}{5}​​

=4925= \frac{49}{25}​​

αβ=75(since α>β)\implies \alpha - \beta = \frac{7}{5} \quad (\text{since } \alpha > \beta)​​

Using identity α2β=(αβ)β\alpha - 2\beta = (\alpha - \beta) - \beta​:

From α+β=35\alpha + \beta = \frac{3}{5}​ and αβ=75\alpha - \beta = \frac{7}{5}​,

2β=(α+β)(αβ)2\beta = (\alpha + \beta) - (\alpha - \beta)​​

=3575= \frac{3}{5} - \frac{7}{5}​​

=45=>β=25= -\frac{4}{5}\Rightarrow \beta = -\frac{2}{5}​​

Now,

α2β=75(25)=95\alpha - 2\beta = \frac{7}{5} - \left( -\frac{2}{5} \right) = \frac{9}{5}​​

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