If $x$ is real and $\alpha, \beta$ are maximum and minimum values of $\frac{x^2-x+1}{x^2+x+1}$ respectively, then $\alpha+\beta=$

The value of $c$ such that the straight line joining the points $(0,3)$ and $(5,-2)$ is tangent to the curve $y=\frac{c}{x+1}$ is

If the percentage error in the radius of circle is 3 , then the percentage error in its area is

The equation of the tangent to the curve $y=x^3-2 x+7$ at the point $(1,6)$ is