(a) Craig is investigating the gradient of chords of the curve with equation f(x)=x-x Each chord joins the point (3, -6) to the point (3+h, f (3+ h)) The table shows some of Craig's results. x f(x) h x+h f(x + h) Gradient 3 -6 1 4 -12 -6 3 -6 0.1 3.1 -6.51 -5.1 3 -6 0.01 3 -6 0.001 3 3 -6 0.0001 Show how the value -5.1 has been calculated. (b) Complete the third row of the table above. [1 mark] [2 marks] ' (c) State the limit suggested by Craig's investigation for the gradient of these chords as h tends to 0 [1 mark] 1 (d) Using differentiation from first principles, verify that your result in part (c) is correct. [4 marks]