MT [242] geometric meaning of images

Set the function $ f (x) = x ^ 2 + ax + B $. Known functions $ f (x) $ have zero points on $ [-] $, if $0 \ le b-2a \ LE 1 $, evaluate the range of $ B $

(2015 Zhejiang liberal arts college entrance examination 20 (2 ))

Analysis: It is understood that the $ g (x) = ax + B, h (x) =-x ^ 2 $ image has an intersection point on $ [-] $. and $ G (-2) \ in [0, 1] $. It is easy to know from the graph that $ p $ is used to get $ A $ points. When the tangent is performed, $ B $ is the largest, when $ C $ is passed, $ B $ is the smallest. therefore, it is easy to know $ B \ in [-3, 9-4 \ SQRT {5}] $

 

MT [242] geometric meaning of images