3. 1+x²/(1+x)²≥5/4
x²/(1+x)²-1/4≥0
(4x²-(1+x)²)/4(1+x)²=(2x-1-x)(2x+1+x)/(1+x)²=(x-1)(3x+1)/(1+x)²≥0
==========-1=====-1/3======1=======
+++++++++++++++++ ------------ +++++++
x=(-oo -1)U(-1 -1/3]U[1 +oo)
4/ (x+6)³(x-4)/(2-x)⁶≥0
===========-6========2=======4========
++++++++++++----------------- ------------- ++++++++
x=(-oo -6]U[4 +oo)