Đáp án:
Giải thích các bước giải:
A=1/45+2/45+1/15+4/45+1/9+2/15+7/45+8/45+1/5
=1/45+2/45+3/45+4/45+5/45+6/45+7/45+8/45+9/45
=1+2+3+4+5+6+7+8+9
____________________________________
45
=(1+9)+(2+8)+(3+7)+(4+6)+5
___________________________________________
45
=10*4+5
_____________
45
=45/45
=1
B=1/28+(-1)/14+3/28+1/7+(-5)/28+3/14+(-1)/4
=1/28+(-2)/28+3/28+4/28+(-5)/28+6/28+(-7)/28
=1+(-2)+3+4+(-5)+6+(-7)
______________________________________
28
=1+(3-2)-(5-4)-(7-6)
_______________________________________
28
=1+1-1-1
_______________________________________
28
=0
#Chiell-))
#Xin_câu_trả_lời_hay_nhất
