- A$\frac{a+b-\sqrt{a^{2}+b^{2}-a b}}{12}$
- B$\frac{a+b-\sqrt{a^{2}+b^{2}+a b}}{6}$
- ✓$\frac{a+b-\sqrt{a^{2}+b^{2}-a b}}{6}$
- D$\frac{a+b+\sqrt{a^{2}+b^{2}-a b}}{6}$
$\Rightarrow \mathrm{V}(\mathrm{x})=(2 \mathrm{x}-\mathrm{a})(2 \mathrm{x}-\mathrm{b}) \mathrm{x}$
$\Rightarrow \mathrm{V}(\mathrm{x})=4 \mathrm{x}^{3}-2(\mathrm{a}+\mathrm{b}) \mathrm{x}^{2}+\mathrm{abx}$
$\Rightarrow \frac{\mathrm{d}}{\mathrm{dx}} \mathrm{v}(\mathrm{x})=12 \mathrm{x}^{2}-4(\mathrm{a}+\mathrm{b}) \mathrm{x}+\mathrm{ab}$
$\frac{\mathrm{d}}{\mathrm{dx}}(\mathrm{v}(\mathrm{x}))=0 \Rightarrow 12 \mathrm{x}^{2}-4(\mathrm{a}+\mathrm{b}) \mathrm{x}+\mathrm{ab}=0<_{\beta}^{\alpha}$
$\Rightarrow \mathrm{x}=\frac{4(\mathrm{a}+\mathrm{b}) \pm \sqrt{16(\mathrm{a}+\mathrm{b})^{2}-48 \mathrm{ab}}}{2(12)}$
$=\frac{(a+b) \pm \sqrt{a^{2}+b^{2}-a b}}{6}$
Let $\mathrm{x}=\alpha=\frac{(\mathrm{a}+\mathrm{b})+\sqrt{\mathrm{a}^{2}+\mathrm{b}^{2}-\mathrm{ab}}}{\frac{6}{\mathrm{~d}}}$
$\beta=\frac{(\mathrm{a}+\mathrm{b})-\sqrt{\mathrm{a}^{2}+\mathrm{b}^{2}-\mathrm{ab}}}{6}$
Now, $12(\mathrm{x}-\alpha)(\mathrm{x}-\beta)=0$
$\therefore \mathrm{x}=\beta$
$=\frac{\mathrm{a}+\mathrm{b}-\sqrt{\mathrm{a}^{2}+\mathrm{b}^{2}-\mathrm{ab}}}{\mathrm{b}}$
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Then $y^{\prime}-y^{\prime \prime}$ at $x=-1$ is equal to