Draw a horizontal line through the $y$ -intercept of the straight-line graph of $\mathrm{Part} \mathrm{B}$, and form a triangle by drawing a vertical line through the last data point.
(a) Prove that the area of the triangle is the work done in stretching the spring. (Hint:
$W=\frac{1}{2} k x^{2}$, and area of triangle $A=\frac{1}{2} a b$, that is, one-half the altitude $(a)$ times the base $(b) .)$