a)\(\dfrac{2}{x^2-y^2}\sqrt{\dfrac{3\left(x+y\right)^2}{2}}\left(x,y\ge0;x\ne y\right)\)

b)\(\dfrac{2}{2a-1}\sqrt{5a^2\left(1-4a+4a^2\right)}\left(a>0,5\right)\)

There is no one that does not know about it.

-> Everybody 

He isn’t satisfied with his son’s school report. (contented)