y=-(5-4x-x^2)^(1/2)=-[9-(x+2)^2]^(1/2)
9-(x+2)^2>=0,-5<=x<=1
递增区间,就是9-(x+2)^2的递减区间
就是(x+2)^2的递增区间（同增异减）
-2<=x<=1