证明二次函数f(x)=ax*x+bx+c(a<0)在区间（-无限大，-b/2a]上是增函数．
热心网友
f(x) = ax*x+bx+c =a*(x+b/2a)^2 + (c - b^2/4a)x = {（-无限大，-b/2a]}时, 若: x1 = x20 = x1 +b/2a = x2 +b/2a(x1 +b/2a)^2 = a*(x2 +b/2a)^2== f(x1) = f(x2)证毕
热心网友
开口向下 对称轴左边当然单调增
热心网友
找抽啊，这么简单
证明二次函数f(x)=ax*x+bx+c(a<0)在区间（-无限大，-b/2a]上是增函数．
f(x) = ax*x+bx+c =a*(x+b/2a)^2 + (c - b^2/4a)x = {（-无限大，-b/2a]}时, 若: x1 = x20 = x1 +b/2a = x2 +b/2a(x1 +b/2a)^2 = a*(x2 +b/2a)^2== f(x1) = f(x2)证毕
开口向下 对称轴左边当然单调增
找抽啊，这么简单