2.在平面直角坐標(biāo)系xOy中,對(duì)于點(diǎn)P(a,b)和點(diǎn)Q(a,b′),給出如下定義:若b′=
,則稱點(diǎn)Q為點(diǎn)P的勤學(xué)點(diǎn).例如:點(diǎn)(2,3)的勤學(xué)點(diǎn)的坐標(biāo)是(2,4),點(diǎn)(-2,5)的勤學(xué)點(diǎn)的坐標(biāo)是(-2,-5).
(1)①點(diǎn)
的勤學(xué)點(diǎn)的坐標(biāo)是
;
②點(diǎn)A(2,a)是函數(shù)y=4x圖象上某一個(gè)點(diǎn)的勤學(xué)點(diǎn),則a的值為
;
(2)若點(diǎn)P在函數(shù)y=x+2(k≤x<3,-7<k<3)的圖象上,求其勤學(xué)點(diǎn)Q的縱坐標(biāo)b'的取值范圍(結(jié)果可用含k的代數(shù)式表示);
(3)若點(diǎn)P在關(guān)于x的二次函數(shù)y=-x
2+2x-t
2+t的圖象上,其勤學(xué)點(diǎn)Q的縱坐標(biāo)b'的取值范圍是b'>m或b'≤n,其中m>n.令s=m-n,直接寫出s關(guān)于t的函數(shù)解析式及t的取值范圍.