B= 20^9+1/20^10+1
B= 20^9 +1 +19/ 20^10+1+19
B= 20^9 +20 /20^10+20
B= 20(20^8 +1) / 20(20^9+1)
B= 20^8+1 / 20^9+1 =A
=> A = B
Vậy...
b) C= 54.107- 53/ 53.107+ 54
C= (53+1)107-53 / 53.107 +54
C= 53.107+ 1.107 - 53/ 53.107 +54
C= 53.107 + 107 -53/ 53.107 +54
C= 53.107 + 54 / 53.107 + 54
C= 1
Vậy...