B
brandnewworld


[TEX]25-30=1-6 \Rightarrow 25-30+9=1-6+9 \Rightarrow 5^2-2.5.3+3^2=1^2-2.1.3+3^2 \Rightarrow (5-3)^2=(1-3)^2 \Rightarrow 5-3=1-3 \Rightarrow 5=1!!!!!!!!!!!!!!!!!!!!!!!!!!!!![/TEX]. Bào Toán sai chỗ nào?