f(x)=2 x2+2x-3=2(x^2+x+1/4)-1/2-3=2(x+1/2)^2-7/2
开口向上,对称轴是x=-1/2.
故当x<-1/2时,y随x的增大而减少,即单调递减区间是(-无穷,-1/2]
同样递增区间是[-1/2,+无穷)