So f(-3/4)=f(3/4)

The other a2-a+1= a2-a+1/4+3/4 = (a-1/2) 2+3/4.

Because (a-1/2) 2 >; =0

so(A- 1/2)2+3/4 >； =3/4

And because f(x) is a decreasing function on [0, positive infinity].

So f (3/4) >: = f [(a-1/2) 2+3/4]

That is f (-3/4) >: = f (a 2-a+1)

2、f(x)= ax+ 1/x+2 =[a(x+2)+ 1-2a]/x+2 = a+( 1-2a)/(x+2)

Because f(x)=a+( 1-2a)/(x+2) is the increasing function in the interval (-2, positive infinity).

So 1-2a

So a> 1/2

So the range of a is (1/2, positive infinity).