1. equation of a tangent

For the function $y=\sqrt{x}$ determine the equation of the tangent at the point on the graph where $x=9$

2. the gradient of that equation at x = 9 is just the derivitive

gradient (m) = dy/dx = 0.5x^-0.5

a tangent will have the form of y = mx + c

and from the original equation can see that when x = 9, y = 3;

using all these values you should be able to determing the equation

For further help see

Tangents and Normals