-3X^2-X+1
=-3[X^2+1/3X+(1/6)^2-(1/6)^2]+1
=-3(X+1/6)^2+1/12+1
=-3(X+1/6)^2+13/12
因为-3(X+1/6)^2≤0
所以原式不大于13/12