[tex]( { - \frac{3}{7} )}^{ - 1} - {7}^{ - 1} \times \frac{1}{3} [/tex]
[tex] = - \frac{7}{3} - \frac{1}{7} \times \frac{1}{3} [/tex]
[tex] = - \frac{7}{3} - \frac{1}{21} [/tex]
[tex] = - \frac{7 \times 7}{7 \times 3} - \frac{1}{21} [/tex]
[tex] = - \frac{49}{21} - \frac{1}{21} [/tex]
[tex] = - \frac{49 - 1}{21} [/tex]
[tex] = - \frac{48}{21} [/tex]
[tex] = - \frac{16}{7} [/tex]