Because -x+(4+x)=4, this function is symmetrical about the straight line x=2. (Let -x be an arbitrary number x 1, and (4+x) be another number x2. Since x 1+x2=4, the positions of x 1 and x2 are symmetrical about the point (2,0), and it can be deduced from the formula that the whole function is symmetrical about the straight line x=2), so b+4a =