first we verify that point A(3, 1) IS on the graph as it verifies the equation
the slope of the tangent is the derivative :
dy/dx = -3/x^2
therefore the slope is
m = dy/dx(3) = -3/9 = -1/3
therefore the equation is :
y - 1 = (-1/3)(x - 3)
-3y + 3 = x - 3