1, chung minh rang ( can a+ can b)^8 nho hon hoac bang 64ab(a+b)^2
2 cho
a,b,c,d lon hon 0
1/(a+1)+1/(b+1)+1/(c+1)+1/(d+1) lon hon hoac bang 3
chung minh rang abcd nho hon hoac bang 1/81
3
cho x1 , x2, x3, ...........xn lon hon 0
1/(1+x1)+1/(1+x2)+1/(1+x3)+............+1/(1+xn)
chung minh rang
x1.x2.x3.x4...........xn nho hon hoac bang 1/(n-1)^n