Let $ƒ\left(x\right)$  be a function defined by $ƒ\left(x\right)=(ab-a^2-2)x-\underset{0}{\overset{x}{\int }}({\cos }^{4}t+{\sin }^{2}t-2)dt.$  If $ƒ\left(x\right)$  is a decreasing function for all  $x\in R$ and for all $a\in R$ , where a is independent of x, then b belongs to