P
phnglan


tính:
A=[TEX] \frac{7}{10}+ \frac{7}{10_^2}+ \frac{7}{10_^3}+ \frac{7}{10_^4}[/TEX]+..................
A=[TEX] \frac{7}{10}+ \frac{7}{10_^2}+ \frac{7}{10_^3}+ \frac{7}{10_^4}[/TEX]+..................