TeX source:
\Delta CS=\int_p^{p+t}x_1(p_1)dp_1=a^{\frac{1}{(1-a)}}\int_p^{p+t}(\frac{1}{p_1})^{\frac{1}{(1-a)}}dp_1=a^{1 \over 1-a}\frac{1} {1-{1 \over 1-a}}p_1^{1-{1 \over 1-a}}|_p^{p+t}