Explanation
$$\textbf{Hence, Option 'D' is correct} $$
At any point $$(k, k^2+8)$$ on $$y=x^2+8$$, the slope of tangent is $$ \dfrac{dy}{dx}|_{x=k}=2k$$.....(1)
Similarly, at any point $$(p, -p^2)$$ on $$y=-x^2$$, the slope of tangent is $$ \dfrac{dy}{dx}|_{x=p}=-2p$$....(2)
For common tangent, $$2k=-2p \Rightarrow k=-p$$
Hence, the coordinates of point on common tangent and on $$y=-x^2$$ can be written as $$(-k, -k^2)$$ as shown in figure.
So, slope of common tangent is $$ \dfrac{8+k^2-(-k^2)}{k-(-k)}=\dfrac{8+2k^2}{2k}$$
From (1), slope is also equal to $$2k$$.
Hence, $$\dfrac{8+2k^2}{2k}=2k$$
Solving, we get $$k= \pm 2$$.
Discarding negative value (since 'k' is positive as defined in the function), we get $$k=2$$
Hence, slope of common tangent is $$2k=4$$
The point common to tangent and $$y=x^2+8$$ is $$(2,12)$$
Hence, equation of common tangent is $$y-12=4(x-2)$$
To find $$x$$ intercept, substitute $$y=0$$ in the above equation.
We get $$x$$ intercept$$=-1$$
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