Find the range of value of $$t$$ for which

$$2 \sin t=\frac{1-2 x+5 x^{2}}{3 x^{2}-2 x-1}, t \in\left[-\frac{\pi}{2}, \frac{\pi}{2}\right]$$

Circles with radii 3, 4 and 5 touch each other externally if P is the point of intersection of tangents to these circles at their points of contact. Find the distance of P from the point of contact.

Find the equation of the plane containing the line $$2 x-y+z-3=0,3 x+y+z=5$$ and at a distance of $$\frac{1}{\sqrt{6}}$$ from the point $$(2,1,-1)$$.

If $$\left|f\left(x_{1}\right)-f\left(x_{2}\right)\right| \leq\left(x_{1}-x_{2}\right)^{2}$$, for all $$x_{1}, x_{2} \in$$ $$\mathbb{R}$$. Find the equation of tangent to the curve $$y=f(x)$$ at the point $$(1,2)$$.