Answer 39 and 40.
39. The shortest distance between the lines 2x + y + z — 1 = O = 3x + y + 2z — 2 and x = y z, is 40. dx is equal to 

$$\begin{gathered} a. \frac{1}{\sqrt{2}} \\ b. \frac{1}{\sqrt{3}} \\ c. \frac{\sqrt{3}}{2} \\ d. \frac{1}{2} \\ 40\int \frac{x^7-x^5+x^3-x}{x^{10}+1}dx \\ a. \frac{1}{10}\ln \left(\frac{x^{10}+1}{{\left(x^2+1\right)}^5}\right)+C \\ b. \frac{1}{10}\ln \left(\frac{x^{10}+1}{{\left(x^3+1\right)}^4}\right)+C \\ c. \frac{1}{5}\ln \left(\frac{x^{10}+1}{{\left(x^2+1\right)}^4}\right)+C \\ d. \frac{1}{10}\ln \left(\frac{x^{10}+1}{{\left(x^2+1\right)}^4}\right)+C \end{gathered}$$