2+13÷13-12÷12+9÷9×9/a÷a+10×a÷a
[tex] \frac{2 + 13 \div 13 - 12 \div 12 + 9 \div 9 \times 9}{a \div a + 10 \times a \div a} =\frac{2 + 1 - 1 + 9}{1 + 10a} = \frac{2 - 10}{10a} = \frac{ - 8}{10a} = \frac{ - 4}{5a} [/tex]
