25.如圖,拋物線y=-x
2+4x+5與x軸交于點(diǎn)A和點(diǎn)B,與y軸交于點(diǎn)C.
(1)求出A、B、C三點(diǎn)的坐標(biāo);
(2)將拋物線y=-x
2+4x+5圖象x軸上方部分沿x軸向下翻折,保留拋物線與x軸的交點(diǎn)和x軸下方圖象,得到的新圖象記作M,圖象M與直線y=t恒有四個(gè)交點(diǎn),從左到右四個(gè)交點(diǎn)依次記為D,E,F(xiàn),G.若以EF為直徑作圓,該圓記作圖象N.
①在圖象M上找一點(diǎn)P,使得△PAB的面積為3,求出點(diǎn)P的坐標(biāo);
②當(dāng)圖象N與x軸相離時(shí),直接寫出t的取值范圍.