BT1:Cho x,y>0. Chứng minh rằng: (3x+3y)(\(\dfrac{1}{2x+y}\)+\(\dfrac{1}{x+2y}\)) >= 4
BT2:Cho a,b,c>0. Chứng minh rằng:
a) \(\dfrac{1}{2a+b+c}\)+\(\dfrac{1}{a+2b+c}\)+\(\dfrac{1}{a+b+2c}\)=<4
b)\(\dfrac{a}{1+a^2}\)+\(\dfrac{b}{1+b^2}\)+\(\dfrac{c}{1+c^2}\)=<\(\dfrac{3}{2}\)