B1: cho a,b,c la cac so nguyen duong
CMR:neu a /b >hoac bang c/d thi a/b > hoac bang a+c/b+d > hoac bang c/d
B2: Tim PS nho nhat khac 0 sao cho khi chia no cho 14/9 ; cho 45/27 deu duoc thuong la cac so tu nhien
B3:CMR: 1/2^2 + 1/4^2 + 1/6^2 +....+ 1/100^2 < 1/2