3.如圖,A,B兩點(diǎn)在數(shù)軸上對(duì)應(yīng)的數(shù)分別為a、b,已知|a+2|+(b-7)
2=0,動(dòng)點(diǎn)P、Q同時(shí)出發(fā),點(diǎn)P從點(diǎn)A出發(fā),以每秒2個(gè)單位的速度沿?cái)?shù)軸向點(diǎn)B運(yùn)動(dòng),當(dāng)點(diǎn)P到達(dá)點(diǎn)B后,立即以原來(lái)的速度返回,動(dòng)點(diǎn)Q從點(diǎn)B出發(fā),以每秒3個(gè)單位的速度向點(diǎn)A運(yùn)動(dòng),當(dāng)點(diǎn)Q到達(dá)點(diǎn)A后,也立即以原來(lái)的速度返回,當(dāng)點(diǎn)Q返回至點(diǎn)B時(shí),兩點(diǎn)同時(shí)停止運(yùn)動(dòng).設(shè)運(yùn)動(dòng)時(shí)間為t秒.
(1)a=
,b=
,當(dāng)t=2時(shí),點(diǎn)Q對(duì)應(yīng)的數(shù)是
.
(2)點(diǎn)P運(yùn)動(dòng)到6所對(duì)應(yīng)的點(diǎn)時(shí),點(diǎn)Q對(duì)應(yīng)的數(shù)是多少?
(3)當(dāng)點(diǎn)P、Q出發(fā)時(shí),點(diǎn)M同時(shí)從原點(diǎn)出發(fā),以每秒1個(gè)單位的速度向B運(yùn)動(dòng),當(dāng)點(diǎn)Q停止運(yùn)動(dòng)時(shí),點(diǎn)M也停止運(yùn)動(dòng).請(qǐng)問(wèn)t取何值時(shí),點(diǎn)M到點(diǎn)P和到點(diǎn)Q的距離相等(此時(shí)點(diǎn)P、Q不重合)?請(qǐng)直接寫(xiě)出答案.