by Tìm số xy−−−−− biết xy−−−−−.xyx−−−−−−−−−− = xyxy−−−−−−−−−−
Hướng dẫn
Ta có: xy−−−−−.xyx−−−−−−−−−− = xyxy−−−−−−−−−−
xy−−−−−(xy−−−−−.10 + x) = xy−−−−−.100 + xy−−−−−
xy−−−−−(10.xy−−−−− + x – 101) = 0
xy−−−−−(100x + 10y + x – 101) = 0
100x + 10y + x – 101 = 0(xy−−−−− ≠ 0)
(100x + 10y + x) = 101
xyx−−−−−−−−−− = 101
