- Home
- Standard 11
- Mathematics
જો $a, b, c$ એ ત્રિકોણની ત્રણ બાજુઓ છે. જે $\left(a^2+\right.$ $\left.b^2\right) x^2-2 b(a+c) \cdot x+\left(b^2+c^2\right)=0$ નું સમાધાન કરે છે. જો $x$ ના શક્ય ઉકેલોનો ગણ $(\alpha, \beta)$ છે. તો $12\left(\alpha^2+\beta^2\right)=$............................
$30$
$36$
$35$
$37$
Solution
$\left(a^2+b^2\right) x^2-2 b(a+c) x+b^2+c^2=0 $
$ \Rightarrow a^2 x^2-2 a b x+b^2+b^2 x^2-2 b c x+c^2=0$
$ \Rightarrow(a x-b)^2+(b x-c)^2=0 $
$ \Rightarrow a x-b=0, \quad b x-c=0 $
$ \Rightarrow a+b>c \quad b+c>a \quad \quad c+a>b$
$a+a x>b x $
$a+a x > a x^2 $
$ x^2-x-1 < 0$
$a x+b x > a $
$ a x+a x^2 > a $
$ x^2+x-1 > 0$
$a x^2+a>a x$
$x^2-x+1>0$
always true
$\frac{1-\sqrt{5}}{2}<\mathrm{x}<\frac{1+\sqrt{5}}{2}$
$\mathrm{x}<\frac{-1-\sqrt{5}}{2}, \text { or } \mathrm{x}>\frac{-1+\sqrt{5}}{2} $
$\Rightarrow \frac{\sqrt{5}-1}{2} < x < \frac{\sqrt{5}+1}{2}$
$\Rightarrow \alpha=\frac{\sqrt{5}-1}{2}, \beta=\frac{\sqrt{5}+1}{2}$
$12\left(\alpha^2+\beta^2\right)=12\left(\frac{(\sqrt{5}-1)^2+(\sqrt{5}+1)^2}{4}\right)=36$